Bald spots

I noticed a couple of weeks ago that my dads cat had a bald spot on his back. We put a sweater on him to stop him from licking it, and a little fur has grown back. But today I noticed that another cat has a smaller bald spot on her head. There is no way she could have done that herself. Another one has allergy problems, but they have been going on a little while and it looks completely different on him so I dont think its related. 

Here are some pictures of the bald spots.



Does anyone have any idea what it can be? I would have taken them to the vet if they were mine, but I am currently having one of my own cats treated for allergies and its sort of eating up all of my money.

It could be food allergies or an allergy to something or even a skin condition. One my cats gets bald spots from a particular pet toothpaste and from Revolution parasite preventative Can your dad take the cats to the vet?