Yes. There should be no problem about both using the same litter box.

Probably. It will go better if you allow them to get to know each other gradually.

Yes. She'll probably be thrilled to be a house kitty again.

Standard shots are rabies inoculation, feline leukemia vac, and a combo vaccine that includes distemper, corona virus and a couple other common infections. Some cats can tolerate all three at once with no problem. I prefer to have the rabies shot separate and a week or so after the others.

Best wishes to you and your new roomies!

They would use the same litter box, but would probably be happier with two different boxes (not that they will use the specified box), but as long as you keep the boxes cleaned often, it should not be a problem. If you do have any trouble, the first step would be to add a second box because it might be an issue. Wait and see.

I have had two cats most of the time, and these were cats who did not know each other prior to living in the same house. I usually keep them separated by a door for a while (I am told it should be a few days, but a few hours is about as long as I can stand the meows before I just let the cats sort it out). Some cats get along fine, some learn to just ignore each other, but it works out either way.

As to shots, etc., rabies is required just about everywhere. The FVRCP shot (distemper and other vaccines combined) is also important. I would take them to a vet and take advise from a professional on what else you might need to do. They will often want to test for some of the more common infectious diseases that they could have picked up. Over the course of my life, I have done all the shots and tests available, and I have at other times passed on things that were not required because of the expense. Do what you can. The cats will be grateful to have a nice home where they will be cared for.

your vet might not want to give all the usual immunizations. Just go with their recommendation. When mine get to be around 16 they get fewer of them because I think it can be hard on them.

go to target buy 2 more boxes, give then space.