As a daughter, how can I help my father who is the caregiver of my mother?

My mother has had a heart attack (6 stints), breast cancer (has beat it) among other issues. She has many doctors and none can find anything wrong with her. She either sits in the chair and watches TV or goes to bed and sleeps for hours on end. She's been diagnosed with depression but she does take an antidepressant. My father does all of the cooking, cleaning, shopping and whatever else pops up. I go to visit and have been for the past two years attending every dr. appt with my mother. She has a constant cough but her pulmonology dr can find nothing wrong with her so he has tried many different things, inhalers, allergy meds, etc. Problem is she doesn't follow through with the meds, just won't use them or has to be told by my father to use them. Basically she has a clean bill of health. She doesn't drink enough fluid during her waking hours (my dad gives her Gatorade and Pedialite) when she is up but it doesn't seem like enough because she starts throwing up (dry heaves). My dad then worries and done this many other times, rushes her to E.R. and they give her fluids through an IV then send her home. Diagnosis: dehydration. My dad cancels appointments for her or decides to change up her meds occasionally and that is very frustrating for me. My dad depends on me pretty much, although there are 4 other children (2 which live out of state). My dad won't ask anyone else for help, he just counts on me. I'm very close to my dad, not so much my mom so I'm feeling the brunt of all of this and I'm very frustrated and I feel guilty as if I'm not doing enough. During her throwing up stages I told my father that if he took her to the E.R. I would not go because he knew what the problem was and how to deal with it. He's an impatient man and he's a reactor. He's a negative person and tells me that all the doctors can't do much for my mom because she's not better. I tell him that they tell him that because there is nothing wrong with her. Is she a hypochondriac? I'm starting to resent her for taking away my dad's life (he has to stay and babysit her day in and day out). She doesn't try to improve. She's done PT and she quits, says it hurts so she doesn't ever want to go anywhere, not even church anymore. If I make a suggestion to my dad about a senior center he immediately dismisses the idea. My dad is not the patient here, but as for me, I'm dealing with him who is dealing with my mother who is the patient and I just don't know what to do anymore. Just stay and listen to him babble on and on about her illness and watch her do this to herself and to him and to me? My dad even said one day that the easiest thing here would be for one of them to just die. I've never heard him talk like that before and it makes me sad for him. She is 79 and he is a very active 83 year old who is missing out on alot of life. My mom has been the sickly type person since her 50's. Does she just like the attention?