This crap is just fuel for gossip. Can you imagine the pioneers out in service, whispering around your sister-in-law. One of two things will happen...she will either she through their unloving behavior, or she will come to be so self-righteous that your brother's marriage will be down the crapper. I hope that this is the catalyst to push her and your brother out.
Tell him we are here for him if he ever wants support.
Leslie