You can call your local Area Agency on Aging and ask for guidance. You can call Adult Protective Services and ask for a wellness check. You can call your local law enforcement (police/fire/sherrif) and see if they will, at your request, send EMTS to examine your mom. BUT, if mom hasn't been declared incompetent, there may not be much they or you can do. You can seek guardianship ( very expensive, requires lawyers, court hearings).
I would probably show up at their door and if mom looked like she was in bad shape, I'd call 911 and request an ambulance for mom. YOUR being there to act as the voice of sanity could be the difference in EMTS obliging and using their persuasiveness to get mom to cooperate.
Babalou's suggestions are very good. It's difficult to know what might be the best option. I would consider seeing an Elder Law attorney who regularly handles Incompetency/Guardianship cases for a consultation. They can give you advice, answer questions and give you a good idea of what proof you might need to proceed. Find out in advance what they consultation fee. It might be worth that investment, even if you don't go the guardianship route.
I would probably show up at their door and if mom looked like she was in bad shape, I'd call 911 and request an ambulance for mom. YOUR being there to act as the voice of sanity could be the difference in EMTS obliging and using their persuasiveness to get mom to cooperate.
Does dad have firearms?