I don't see how they would interfere with your feral kitties. The most aggressive thing
I've seen them do is hiss.

We have them all the time, and our cats just stand there and watch the
possum walk by. Mother possums carry their young for quite a while. When the babies
get to be the size of rats, she will park them in a bush/low growing tree and leave them there
when she goes to eat. We found some babies once that way.

If you really want him out--(we had a raccoon once do this)...
put the food out in larger distances away from the garage and you will
have to stay up and when she comes out finally (when the food is a ways away),
you make it impossible for her to return. Make sure there is no hole on the backside of your garage...they dig you know. We had one under our study here one year.

Once she learns you are putting food out, she will come forth quickly, and venture farther and farther out. That is when you get her. You can rent HavAHART live traps at some hardware stores, and you could trap her too and drive her to a less populated spot and release her. You might have an old, sick one in there, who is going to be resistant to coming out. You'll just have to see.