They’ve got an abundance of insects somewhere, they’d do well to leave the egrets be. They will move on when the food source is gone. A flock of cattle egrets can eat a lot of crickets, grasshoppers and grubs. As to a health hazard, that just isn’t likely. I spend a lot of time around wading birds, it sure hasn’t hurt me.
I also like rookery areas, but a residential neighborhood is no place for one. The stench is something else, for one thing.
The reasons they were there:
1. Substrate - something on which to build a nest.
2. Freedom from predators - not too many predators in a residential area.
3. Food within a reasonable flight radius Texas has lots for a bird to eat.
Nice tall trees were the first attraction, IMHO.