Cats will sometimes overgroom as well because of the stress. One of my cats became very depressed when I lost her companion kitty. She overgroomed, was lethargic, not eating enough and basically looked sad. Not at all her usual self. Took her to vet. I started giving her Rescue Remedy (homeopathy) for a while as well.

One thing that might happen if there are a number of cats suddenly sharing the same area, is that your own cats might start marking their territory. Even if they appear to be friendly this can happen, and even if they've never done it before inside the house.

I'd do what mrsd suggested about using their own bowls etc., would be a big help. I'm sorry it's such a difficult time for you to do this, but as already suggested I'd be bringing over one of your daughter's rugs or floor mats or something like that, so that the cats have something very familiar with them.

(((Di)))