How long will mother cat grieve and call for kittens?

Hi,
A mother cat with her two kittens (I guessed them to be about 2 months old) and already pregnant again arrived at our home looking for food. I put out a bed, food and water for her and the kittens and treated them for ticks and fleas. The kittens were surprisingly tame and mother cat very cautiously allowed me to touch her. I found this to be very strange. I fed them outside our yard as our dogs would go crazy at the fence when they saw the cats. We returned from a weekend away to find that the three cats were no longer there. This after they had been sleeping in their little house I put out for them for about 2 weeks and our domestic worker put out food that weekend we were gone. I returned to find other cats eating their food. 2 days later I found one of the kittens all alone in a bush down the road and picked him up and took him home. Two days after that the mother cat returned, but without the other kitten. I don't
Know what became of it. I looked for it for days, but no sign. Long story short, I took the remaining kitten in and managed to couch the mother to get in at a window to come eat. She ended up staying inside with the kitten. We introduced them to the dogs and everything went very well. We had to new additions to the family.

One day our domestic worker called in a state, two of the dogs had gotten hold of kitter (the kitten, at this stage about 4 months old) and he didn't make it. I don't know why they suddenly did that, but our hearts were shattered into a million pieces. My husband and I had grown to love that little thing dearly. 2 weeks after Kitter was killed Mother Cat gave birth to her next litter. 4 beautiful little things. I immediately started looking for homes for them as I was now convinced my dogs would do that again and that I couldn't repeat losing another one in that manner. So early on I have had 2 homes lined up - two kittens to each home. The only good homes I could find are very far. Yesterday I got a lift for two kittens (male and female) to their new home 400km away and had to take the opportunity. I put them in their carry case with their blankets and toys and sent them off. They are now 9 weeks old. Besides the fact that I have been crying since they left, the mother cat has not stopped calling and looking for them. How long will she do this? It also doesn't help that they say Tigger (the little male) is very stressed and hiding all the time. I am heartbroken and now feel like I should just have kept them. The remaining two kittens are due to go to their new homes in 2 or 3 weeks time and I don't think I can repeat yesterday especially since i will have to put these two on a plane to their new home. I am really considering keeping them with me and maybe adopting two kittens for the lady I promised them to. I have been keeping them separate from our dogs up until now and only take them outside to play when my husband takes the dogs for their run. Am I being selfish? should I rather let them go? Heartbroken about letting them go, but don't want to keep them locked up either?

About a week. Hopefully not longer.  The only to do is to try and show her your sympathy, be with her.  Like a cat friend would do.

She has anyways two kittens left, so it makes the loss stepwise, and thus - somewhat easier to carry...   Breeders also use this trick - not all at the same time.

You can also try and let her be a foster mom to orphans??   Make sure they are not carrying contagions...   Even if your mother cat must have reasonably good immune system - otherwise she would have perished when being homeless.  So she must be sturdy above average.

Ps.  And of course, now its high time to  spay her, now when she is done with nursing.

Re  the other questions - you must do as you feel...  There is no good answers from any advisor.

Re the dogs...   Home dogs seldom attack a home cat. But it may happen.   One possibility is he was quite new for them, so although they tolerated him, he was not yet felt as one of the home group, home pack.

Another possibility is it was a play who got astray.  Perhaps the kitten even began it itself, as a play hunt - run after me if you manage!   And the dogs excited suddenly become a mini-pack, get eager and excited each other - and thus, it happened...

We have somewhere an article on what dog breeds who may be problems with cats.  So for example, hunting dogs is a well known warning sign:  their hunting instinct can quite easily be triggered by the hasty movements -  the cat is either running around, or even - begins the whole of it as a play...

So accidents do happen even with quite wellbehaving dogs, your own dogs are thus no monsters.

Just to try and keep on socializing them together, be sure they are good friends, at least in normal circumstances.   And be sure the cat has uncut nails, so it can teach them necessary lessons if it will be needed.  

The best results are when the cat is on the level above the dogs, so they respect it.

Dogs ARE pack oriented animals.  When they see the cat is a part of the pack, under the owners protection and care, they accept it.   And later on, with a little luck, become good friends, and maybe themselves protectors.   Perhaps against other dogs.

Good luck!  @Deeds