If you have a plastic storage box you aren't using or an old plastic dish tub (you know, the kind you put in your sink to do dishes in) they would be perfect for a litter box. With normally two cats it's a good idea to have two boxes anyway.
Do your other cats sleep in your room? If not then the kitten could share your room for a few days. Or a large closet. Really, the kitten doesn't need much room to be happy if it's only temporary. Sounds like things are settling down. That's great! Cats tend to do lots of posturing and silliness for the first day or two.
If you would like to try something that makes them smell familiar you could try a dab of vanilla under their chins and on the base of their tails. They don't need much. Just a touch.
If you are interested in reading how to introduce cats there is a wonderful website. It's http://www.squidoo.com/multi-cat-management
. It's an interesting site to read even if you just want a good read.
Thank you for bringing the kitten in. You are his