Mom has neurologist appt. in May. How to convince Dad to let me go? Mom wants me to. I have so many questions!

Funny, I was trying to put this as a post on my wall but hit the wrong button-divine intervention mayhaps? So I will go with it. :0). I really, really want to go to my Mom's next neurology appointment and ask a whole bunch of questions but I just know my Dad will take it as I don't think he is doing a good enough job with Mom. And he is right. It is not that I think he is doing a bad job just - that he needs help -more than he is willing to admit - and he Is being very very stubborn!!! He is almost being oppositional just to be oppositional. Like when Mom was down at my house last I got her a transfer bench for our tub for her. It is bigger than the one she has at her house and she doesn't have to step over the tub to sit on it as it starts outside the tub and she can sit on it and then swing her legs over the tub and scoot a bit. It worked great!!! And was not cheap. And she rally wanted it to take home with her when her visit was over. So my husband somehow got it in our over stuffed car -she brought a lot of stuff along for the stay -which is fine just it was really hard to get that bench in- and she took it home. The minute my Dad saw it he just was like- "what- don't need that-we have the shower chair!". I told him how I was worried about Mom stepping over the tub side and how well this worked and how she liked it so much at our house she wanted it. My husband put it together and put it in their bathroom as Mom wanted but after her bath she said "I can't use it. I can't scoot on it .". I KNOW that is my Dad talking!!!she totally loved that bench when she was here and used it great but somehow my Dad convinced her it was no good. BUT WHY? Because I suggested it and he HATES not being in control! It makes me soooo mad!!!! And yeah, I get it , he has his pride and all but he needs to stop being so stinking proud. He wants me to help-I want to help --but he won't see things from any perspective but his own and his own is not all that great.
So - this lat month I kinda let him and Mom go. We have been having one heck of a time with my daughter. As I have mentioned she has special needs and behavior is probably the most challenging of her needs- well, there are several health worries that , of course, take presistance but we do all we can for those and then let God do the rest. But , anyway-her behavior-and I know ,at 16, behavior is an issue for a lot of parents but this is different. We have her in therapy and going to a psychiatrist and still we ended up in the ER because she was so out of control we could not keep her safe. Hitting, spitting,-oh -the spitting-she has tics so it is a tic but also behavior- I cannot tell you how many times I have been spit at right in the face-, pushing, yelling cussing... So hard--and so common for her syndrome. So, yeah, it has been a tough month and I just , well, I just didn't have the energy to deal with my Mom and my Dad. Yes, my Dad. He is the "typical "one but my Mom is actually handling her diagnosis better!!! She wants help. She understands that she needs more help. HE won't change. Oh, she can drive you batty, but at least she knows she needs more help.
So , again, sorry I am rambling, I have not been helping them at all this last month -sometimes I feel I help just enough to let him think they can do this without in home aid and other resources -so part of me wanted to see if my stepping away for a month would make him realize her needs more in home care. Let him flounder for a bit. And because I was exhausted from trying to help my DD. still am. But, of course , I feel guilty and now that Mom has an appointment in a couple of weeks I am wondering ifI can convince Dad to let me go. (Mom wants me to go) He must need a break. I can bribe him. Tell him I will come up for a long weekend and he can go gamble( his only pastime , unfortunately) if I can go to the appointment. And then once I am there I am going to interrogate this doctor!! I don't trust him. I will pay heck for it by Dad but I am sick of being kept in the dark!! I know that the doctor suggested more neurological tests that haven't been done. Why not?!?!

So, let me have it. What should I do? Am I a horrible daughter for letting my Mom go a full month ? Come on, Ferris, you must have an opinion? TerriM? How bad of a daughter am I?? Just teasing you, guys!!!! ((hugs))
Any suggestions in how to get my Dad to stop being so set in his ways? We were going to have an intervention but my siblings have kinda disappeared. *sigh- that seems typical. And just what should I ask the neurologist if I do get in? HELP!