As compared to our polygamist cults and multi-generational incest families here in America, they seem tame by comparison. Fathers marrying their daughters (while still staying married to the girls mother) hardly ever make the news anymore.
As far as how the churches should react, in the Jeffs family, they are their own church.
How far can they go, well you heard the authorities just rounded up over 500 women and children in Texas the other day, didn't you?