Again, exhume the bodies and search for abuse. If there is probable cause, this shouldn’t be to hard to get a warrant for.
When you have a closed sect (I don’t believe they get a whole lot of converts - perhaps I’m wrong, but they tend to shun the outside world) you wind up with a very small gene pool. One of the side effects of a small gene pool is deformities and infant deaths. Frankly, I’m kind of surprised we haven’t heard of hemophilia in the males.