My niece-in-law is a troublemaker!?

She has accused my in-laws of ual and physical abuse of her and her daughter. She has taken them to court to keep her children away from them. She is my in-laws granddaughter and her children of course are their great-grandchildren. They have spent most of their retirement money on defending themselves in court and moving her from place to place. No matter what she does to them they keep welcoming her back into their lives. She has told my in-laws a story about my daughter that isn't true and they believe her. They tell us that she wouldn't lie to them. They have been to court to defend themselves against her! Should I take the statement "she wouldn't lie" and believe that her accusations in court were true? Should I believe that my in-laws are ual abusers? I hate family drama and I've tried to reason with them but they refuse to believe my neice is lying to them about my daughter. I'm walking away from them but I feel bad because they're old and may not be here much longer.