For me it's easy.
If BL hurt/killed Gabby, he doesn't deserve protection from his family.
If he left Gabby in the middle of nowhere, possibly without a phone and wearing just the clothes she was wearing and 16 days after arriving home she is still missing, he doesn't deserve protection from his family.
If he is doing absolutely nothing to help find Gabby, he doesn't deserve protection from his family.
Most parents who love their children don't protect them in every circumstance. Some parents shop their children, even in murder cases.
They know Gabby, she lived with them for 2 years (I believe). If they are protecting their son despite the fact that a woman who had plans to join their family is missing, then I can't help but conclude that Brian's actions are a learnt behaviour and they're as bad as he is.