First of all you should get your dog fixed. You don't seem to be breeding for the right reasons. If you have room for another dog save a dogs life instead of killing more.

You dr. is wrong, getting him fixed will help him pottying in the house.
Since he is older it might not help as much as it would a puppy but it will help.

I just don't know how to keep other peoples dogs out of the yard so she wont bring in there poop and eat it on our couch........yuk.
A fence? And check your dogs mouth before it comes in...

1) he will eat all the food
What do you mean by this?
Your dog eats your other dogs food? If that's the case just feed them in different rooms.

The answer to these questions are pretty obvious