Unfortunately, leash laws don’t usually apply to cats. I suggest he start hosing them down and sprinkle repellent on his property. Cats (and some cat owners) are arrogant, but they’re not stupid. Having said that, we have a cat who likes to be outside. I would rather keep her in the house, but my husband coddles her. Even before he started letting her go outside, we had frequent cat visitors. Our cat is spayed, so I guess they just like to visit. Anyway, if someone wants to hose down our cat, more power to them. She needs to stay in her own yard or the vacant lot next door.
Where I live leash laws apply. There are no exceptions for cats.
Further if they are ferals there are laws about that as well.