Help. I have adopted a new cat.

my sister rescued a kitten they saw in the middle of the road. Hes very silent and eats just fine but not that excited when i hand his food.

anyway he's skinny since i can feel his spine, bone legs, and ribs, we had his first deworm this week and his stool doesnt have worms on it.

we isolated him because we also have another kitty with us and we dont want him to be infected too since that kitty is already dewormed and doing just fine now. 

how long should i isolate the new kitten? seems lonely for him to be alone and i cant give my full attention since i have school. thanks.

You didn't mention if he had the FVRCP vaccine shots ? 

Also, I always test my newcomers for FIV (kitty AIDS) which is a simple blood test.

Usually comes back in 3-4 business days.

Use that time for scent or site swapping, to allow the established cat to get used to the newcomers scent.

We kept them separated for between 7-10 days, barring all tests coming back good.

Is the other cat up to date on vaccines? If so, they should be fine to mingle, but the initial introductions need to be supervised.