Even if they didn't carry toxoplasmosis or other zoonotic parasites or diseases, cat poo is just gross.
The horse and chicken manure I use in my garden is composted before planting. And just for the record I'm not crazy about chicken poo either. But when it's been composted and mixed with leaves and other compostables and broken down it's not so repugnant.
As for taking the cats and having them tested that's impossible. Some of them belong to the neighbors and come to eat with them when my mom feeds them.
The best solution I know of to get rid of the filthy things and put a stop to it is to trap them and take them to the pound but my mom just want go for that.