No, definitely don't think you're being too negative.

One of the first rules of rescue is know your limits. There are always discussions on TCS of "how many cats is too many?" And the answer is the same - the number you can comfortably care for, emotionally and financially. For some of us, that's one. For others, it's 32. For most of us, it's 2 to 4.
We can't rescue them all - and that's why TNR exists in the first place.

It's the best of a lot of poor options, basically.
And it can be difficult to find them homes, especially if you're not networked. So if getting stuck with them is a concern, best to TNR them. First and foremost, you have to consider your existing pet kitties.

One last thing before getting to the outside cats. For the allergies - I also have asthma. My doc prescribed advair in addition to the inhaler. We don't have insurance any more, and it's very expensive. It was even somewhat expensive with insurance. I don't know the system up there. But it's something your BF may want to ask his doc about, because using the advair MAJORLY cut down on the amount I needed the inhaler.

And because I was highly allergic to the cats, I have a lot more (non-medication) tips if you think BF might benefit from them.

OK, all of that said...

The dog house sounds great! It's definitely a great starting place.

I'll see if I can find JTBO's post about the shelter she made for her ferals last winter. I think a Finnish winter might be comparable to a Manitoba winter. I know she used a very thick insulation, and it worked quite well.
As to the other subjects/questions:
If you can see she looks pretty pregnant, she's most likely too far along to be spayed anyway. As to what to do about the kittens, there are several schools of thought, and what you choose really depends upon whether you're going to foster them/adopt them (or not).
1) Bring pregnant mom in to have her kittens inside. This is the best way to socialize the kitties, and feral females often don't mind being inside to have their babies and raise them. Sometimes the best thing is to just release them after that: sometimes they learned through their kittens - far more quickly than a normal process of socialization - that people are good, there to help, and inside is OK. That's a coin toss LOL.
2) Let mom have the kittens, and nab them if you can and raise them yourself (the worst of the options IMO).
3) Let mom have the kittens, and let her raise them. Fostering is still an option.
Because of our space issues and the fact that we live in a rural area that is safe for cats (no natural predators, not a lot of cars or traffic), what Gary and I have done when pregnant females that we can't have spayed turned up (which, thankfully, hasn't been often), we let mom make her nest wherever she's going to make it, and raise her kittens however she's going to raise them.
If getting her into a foster network is possible, we've done that. She has her kittens there, and they all get adopted out. Works if mom is young enough.
When that wasn't an option, we let mom have the kittens, and because we can't foster (for a lot of reasons, not just space, but that's a consideration), we let her raise them. We don't try to find the nest - she'll just move them. Feral cat moms know what they're doing, much better than we do. We just keep putting out the food and water, and she brings the kitties to us (the food source) when she's weaning them.
It is natural for moms to push their kitties away at about 12 weeks old. Kitties are still easy to socialize at 8-10 weeks old. So taking them in to socialize them at that age is still an option, if you think you can get them adopted out or don't mind having them live with you until you can find them homes (which gets harder as they get older) - or if you don't mind having them live with you, period.
Socializing them outside is a long process. And then it's even more difficult to adopt them out - because they're not so socialized to "people" as it is that they trust
you. And they've never lived inside - and that turns their world completely upside down. Cats that have only lived outside don't know inside is good.

That's the point of fostering - you turn outdoor cats into cats that can make good pets. Otherwise the requirement for rehoming them is more difficult.
That said... if having them inside longer term isn't really an option... then you really don't have a choice.
Our experience is that they become more friendly once spayed/neutered. The older feral momma should be spayed once you know the kittens are 10-12 weeks old. The kittens should be spayed/neutered as soon as the vet will do it. It is safe to spay/neuter them as young as 8 weeks, or once they're at least 2 pounds... but vets not familiar with this are usually very hesitant to do it - and have no experience spaying/neutering animals that small anyway. The absolute latest they should be spayed/neutered is six months. We never like spaying/neutering during the worst of winter, because we don't like bringing them inside from below freezing to a warm clinic, then putting them back out to below freezing. So we like to trap them either before it's really cold - or once it warms up to above freezing.
In our experience, after being released from the trap after being spayed/neutered, they're back the next morning or evening for food. The only time "our" ferals have ever disappeared for several days is during storms.
Right now we have six active cats in our TNR colony. We trapped... 11? 15? (I'd have to look it up) this spring. Several of the younger ones went into a local foster network. We haven't seen any of the older ones since the advent of summer. We'll find out once it gets cold how many are still around.
Of the six that are regulars, four are here for each meal every day. One got friendly so fast, he was dumped or a stray or something. He doesn't seem to know what toys are, so I think he was maybe a barn cat somewhere... or just somewhere around really friendly people. The other three we know who the mom is and they were born here. (We did finally trap mom too). Of those siblings, a few months ago, one of them "learned" from watching me interact with Baloo (the friendly guy), and she started rubbing around my legs (and making it impossible to walk outside to put food out.

). But she warmed up to hands and petting pretty quickly, and she started talking, and now is just the cutest sweetest thing ever. (All black with a little dot of white on her chest. Her name, of course, is Little Dot). I really want her and Baloo in homes. But they're not cute young kittens anymore, and I can't say they've lived inside, so I can't just "advertise" these cats for adoption portraying them as great indoor pets.
Personally, I find myself worrying about the ferals more than the inside kitties.

But I agree with Willowy - using a live trap is the best way to do it. They don't associate you with the process. And sterilizing sooner rather than later just helps the process. They lose all those hormones that make them spray and be aggressive, and they "friendly up" more quickly without all that craziness. The males don't wander off because they're looking for females, and the females aren't howling because they're in heat. Just like it's SO much better to get your pets sterilized asap, it's better for them, for you - for everyone - to get the ferals sterilized asap.

Finally, as to your question about Moses. Charging off other cats is totally normal. Feral cats tend to be more social than many indoor kitties are - they're used to be around other cats, some of whom come and go, and sharing a food source.
Cats are totally territorial animals by nature. When introducing cats to each other, it's a process exactly because of that. We never had a separate room to use for socializing or introducing new cats - but last year, when we had to bring in Chumley, we actually rented a trailer so he COULD be separate while we went through the process of socialization and him living inside before we started bringing him over here to slowly introduce him into this space. He went into the trailer in May, pending a spot in the foster network. That opened up a month later. We dropped him off at the vet to get his distemper shot (we don't bother with distemper for ferals, because it requires a 3-week follow-up, and we're not trapping again after 3 weeks for that) and to check him for FIV/FeLV. Well, he turned up positive for FIV. So the foster network couldn't take him. So back to the trailer he went. I think it was another month before we began bringing him over here. We focused on scent-swapping between him and our cats for that month. Then we brought him over for 15, maybe 20 minutes. Not to meet the other cats, but just to check out some of the space. We brought him over for a little longer each day. I think it was 3 weeks/a month, then he just never went back to the trailer.

So the process didn't focus on the cats meeting each other so much as it was introducing him to the scent of our cats, and getting our cats used to his scent being in their space and associating that scent with "good" things (treats, brushes, etc.).