My husband is a primary caregiver, but his parents' estate has been left to all other siblings. What can we do?

My husband has always been the one to care for his parents, even though he has 6 other siblings that live closer. He has been gone over 6 wks with his family, and is being the full-time caregiver for his parents. He had his dad sign a power of attorney form a while back too, but the other siblings are mad about it. We found out recently too that one of my husband's brothers has coerced my inlaws into signing a will that leaves everything to himself. We also found out that this guy did a "quitclaim" deed, and my inlaws GAVE him their home. My inlaws favor this son, and NEVER want to ask him to do any of the caregiving duties. My husband left me, his job, and his life behind to care for his parents, who, by the way, have NEVER loved him. They have been using him as a taxidriver/caregiver, but have rewarded the other son with their properties. This brother in law also has a girlfriend who has tried "funny business" at the bank with my mother in law. Basically, they have been trying to "brainwash" them for years, yet do not care for them at all. My husband does EVERYTHING for these people, but my brother in law is rewarded. We filed a police report on my brotherinlaw/girlfriend too, and we think he "paid" the cop to "go away." It is in a border town, where everything is corrupt. I talked to this cop, and he told me that he thought my husband was just being jealous, and greedy. Isn't this elder abuse? We cannot get any help, and my husband is being used by his parents. Can the will be voided? My father in law has dementia, and mother in law is all for her "favorite" son, who is not my husband. She just wants my husband to be the caregiver, but has no intention of leaving him anything.