Are you working with a rescue or TNR group? Or is this something you're doing on your own? Will you be adopting them or are you fostering them?
...as to the rest, well.... the first thing we do when we have kittens in a trap is get them to a vet. We already have arrangements set up whereby we don't need an appointment, we just drop them as soon as we trap them, and the vet calls us when they're ready to be picked up. They could be carrying any number of diseases that you definitely do not want you existing pets to catch. Are they flea and tic free? They probably have internal parasites that need to be treated.
And at five months old, they could have that hormonal shift, so they DEFINITELY need to be spayed or neutered as soon as possible! And they need to be vaccinated. And since you're not going to be releasing them, they ought to be tested for FIV and FeLV. Do you need help finding a low-cost place? Are you in the U.S.?
But at five months old, if born feral and raised by a feral mom with not a lot of people interaction, be prepared to turn off any kind of clock you've got in your head about how long it will take to socialize them! Depending upon their history of interaction with people, it could take some time.
Do you have a cat proof room ready for them where they can spend a couple of months? I don't know how long it will take to have them interact with your cats - but they may need their own room for a few months anyway. They should have places to hide but where you can get at them if you need to, any window screens or sides of air conditioners or whatever should be INSANELY secure...
Are you already armed with Feliway spray and harp music? Flower Essences - preferably Bach's Rescue Remedy?
I'll go find a link to a thread that's currently active where we're talking about socializing, because it is all directly appropriate here.
But they do need to see a vet for a check-up, vaccinations, definitely a spay and neuter at that age and likely parasite treatment before you can do much of anything.
But this is a wonderful, wonderful thing you're doing, and it is SO rewarding!