A strange situation between me, my mother and my grandmother. Any advice?

I am the only one who visits my Grandma in the nursing home. Her daughter, (my mother) & narcissist who appears not to care. She is also suspected of sneaking funds & does not seem to have her mother's best interest at heart. My Grandma is very high functioning. Has been diagnosed w/ dementia, paranoid personality disorder, & delusions. I see Grandma alot. Her daughter doesn't even go see her. She does not stick up for my grandmother at all. Grandma is basically my best friend & vise versa. I am the only one my Gramma can trust & when things do not "appear” correct (money missing, bank statements, other things) it is very easy for ”others" to just say that my grandmother is making things up, or lying. The nursing home believes anything my mother tells them. I don't see much difference in my grandmother's mental capacity, but she was diagnosed with NO tests. She cannot hear well which also appears at times that she isn't quite normal. But I know her...she doesn't seem to have dementia. (My mother also has my Grandma's bank cards & credit cards). A small example....My Mother told me that she had to withdraw over $500 from Grandma's acct.to give to the nursing home for the payment. The same month, my Grandma told me "the billing lady came in & wants her to write a check for the same amount for the same thing". I inquired about this situation to my Mother. She said she would find out what's going on. Minutes later....my mother called back & said "she's making it up, it never happened". A very easy explation for missing money. My Grandma also said that"someone" went thru all her stuff when she wasn't in her room. (Was said to be paranoid, or a delusion). However...my mother told me the "billing"woman said that she had gone to my Grandma's room when she was in the dining room & went thru all her things looking for a bank statement. So it was true. The "billing woman" never told the nurses what she did, which explains my Grandma's claim.So when my Grandma was telling nurses that "someone kept getting into her things"- it's written down as paranoia, & delusional behavior. If the nurses (or anyone else) goes in to speak to my Granndma, IF she can hear them (she is almost deaf), she is capable of carrying on a normal conversation. Also...Grandma is 93. So, it seems to me, (I know her best)..that anyone who interacts with her, is thinking of her age, not her mental state - "as if she is declined mentally". Her room is in the "dementia ward" where many other patients lash out, wander &/or cry out on a normal basis.I see staff act with her as they do the other patients. My Grandma makes perfect sense if ya sit down, & spend time talking with her. But she cannot hear much & her responses look like a severe mental condition.

(Bear with me)
The reason I am explaining all these tiny details, is to give an idea of what is going on "all the time". I do know that my Mother signed her in as long term. Grandma is getting lied to, (theraputic lying?) led on about going home, & intentionally patronized by staff. They treat her the same as other severely declined patients. Being new to this facility, & being aware of her surroundings, makes a very angry woman. That also adds to the appearance of extreme mental decline. I know my Grandma...& aside from normal aging issues, she appears very normal to me. She remembers things that even I forget! 
I've seen this for months now, & my part is to be there for her, love her, & make sure she is being treated with respect, honesty, & compassion. I truly believe she is being taken advantage of. I'm very upset & confused.
Thank you for listening. I tried to give details as well as examples, & descriptions. This situation makes it hard for me to carry on even somewhat normally. I'm having a difficult time eating &sleeping. Yet my mother is living her life as usual, with her husband, who is known to dislike my Grandma. My mother has moved her own family into the background.But my job is to take care of my Grandma. I hope I have explained enough to give some inclination of what is going on. A very strange, seemingly WRONG situation. I am basically the only "adult behaving" member of my family, as is my Grandma. I am not even sure what to do next. I will add tho, how she ended up in a nursing home. Her & my Mother have fought for years. But my mom always seemed to care. Last day of Grandma's freedom...my mother went to my Grandma's apt, where Grandma has taken care of herself for over 30 years. Grandma had enough...she gently, but very firmly pushed my mother out the door, telling her to leave. My Mother called the police - said my Grandma was finally mentally out of control. Grandma was pulled out of her apt by the police. Put in the "city hospital"where they medicated her too much. It was awful. Then.....she was transferred to the nursing home & lowered the meds. Now, they will not let her out. It almost seems more like kidnapping than a caring, move to a nursing home because of dementia?

Im glad to be here, and looking forward to interacting. Thanks so much. 🙂