Thats what happens when irresponsible cat owners do not get their cats neutered.. If you can't afford to pay the vets bill to have it done, then don't own cats. I have 2 cats (both neutered) and I hate it when I see the male toms come snooping around, spraying and being aggressive. And the females howling at night. People are so stupid.
Kudos for taking them in, at least they weren't put in a weighted bag and dropped in a river or lake somewhere... I am sure that goes on too. poor animals.
If you worry you die, and if you don't worry you still die..... so why worry?