What should we do if our Dad is taking my mother’s pain pills on top of his?

My sister the caregiver and her sisters know that their Dad is taking way too many Hydrocodine pills on top of taking their Mothers also leaving Mom not to have what she needs for her pain. What action can be taken and where does my sister and other sisters go to talk to about this and get help for their 85 yr old Dad?? Our Dad is getting meaner and meaner running everyone off by being very rude and ugly and making up lies about everyone he meets. He even accuses several of our Moms bathers of sexually playing with our Mother when they bathe her. Its getting worse. Our Mother is getting more and more mentally abused and has gotten to where now she is defending him. I told my sister I believe its because after everyone has left she has to be alone with him and doesn't want the abuse. They've been together for over 62 years. Our Dad has always been a control freak but its gotten worse.He always has that crazed look in his eyes like everyone is trying to take advantage of him and he's very defensive to the point where its crazy. Our Mother is on Hospice as she has a bladder disease with a cathether and she has other health problems and is in a wheelchair and can't walk. Our Dad can barely walk but refuses to use a cane because of his ignorant pride. He has already broke one hip in the past. Both are getting more and more forgetful. If my sister didn't go over there and wash clothes and cook and among LOTS of other things, they would already be in a Nursing Facility.My parents have stolen years off my sisters life with her husband and teenage son and her hair is falling out. Please tell me what we can do or who to talk to to have our Dad evaluated mentally without him knowing about it. He's very suspicious about everything. We love our parents but something bad is going to happen if we don't do something soon. Is there anything we can do? Neither parent will sign a Power of Attorney form or Medical Form for any of their 5 grown children. As far as assetts, neither of our parents have anything of value except the small lot that their house is on which may have to be sold to provide for them later. The house is in such need of repairs and electrical stuff it would be torn down as it would cost too much to repair. Please tell us whom to get in touch with in FortWorth Texas area, PLEASE ! ! ! Any advise or help will be greatly appreciated. We love our parents and want wahts best for them but I see a decline in my sisters health. She needs help with them. Like I said our Mother is on Hospice( age 79 ) and she has help when needed but the biggest concern we have is our Dad and whats he's doing with our Mothers pills and his hostiilty toward everyone. There are times when all he does is nap and he also smokes and burns holes in everything. Thats real scarey too ! Sincerely Yours;
Sherry Chenault