When he won't or can't sign forms and she can't be power of attorney? He doesn't want to live at a facility, won't go to the doctors, won't take his meds, is in a lot of pain, and now my Mom is too ill to care for him, nor able to perform duties as power of attorney, conservatorship, or probate. Neither my Mom, nor step-Father can afford help, as in a lawyer.
My father wasn't open to any help or advise about anything legal or financial or related to estate planning until it was absolutely necessary and I had things to show him proving he could not take care of things anymore on is own. Then after agreeing he would not follow the plan. Sometimes it would undo or lock down things so I could not pay his bills. I had to severely disable his car when attempting to prevent him from driving. Anyway, a first step is to kindly suggest that you do things for them. Eventually you may gain enough authority to make arrangements and eliminate many steps before you ultimately have to persuade them to do something of the utmost significance like moving from home to a care facility.
Best to you.
Another possibility is if your stepdad is prone to rages, and he won't see a doctor, call 911 the next time he has one and see if he can be admitted for a psychiatric emergency. I know it's not nice but it sounds like your mom is at risk. You have no control over your stepdad and he is non-compliant with dr's recommendations for whatever reasons (dementia or ego?) Caring for someone like that will wear your mom down fast and I would try to focus on getting her safe and properly cared for. Have you discussed your stepfather's condition and the toll it's taking on your mom with her primary doctor?
As Debdaughter wrote, fiduciary is a financial responsibility. If you, your mom, or another family member isn't up to it, the VA can appoint someone to handle it. You need to be able to keep track of his VA income and how it gets spent, so if you are already maxed out, it is fine just to tell them you don't want that role. You don't need to do physical work of caregiving, but need to be able to keep track of receipts/paperwork if someone else does shopping, bill paying, etc.
I'm not clear on what benefits your mom and stepdad are already receiving, but your mom may be eligible for Aid and Attendance if she isn't receiving it already.
I know you would hate lindy's solution but that might be something you might have to consider, but let me go back, you say your dad won't go to the doctor but if he's in the VA system, as you say, he has to go every so often to stay in it, so does he and just that's the only time he'll go? when my dad fell and broke his neck and was sent, not to a VA facility, since the one he would have had to go to, since his couldn't handle it, was so far so he was allowed to go to an outside one, but placed in a C-collar, and was giving me fits, that's what I was told I would need to do if I couldn't handle it but I was able to get him calmed down. I, too, am wondering if you've discussed this with your dad's primary VA doc but I know, too, that in the case of hub's uncle she just brushes it off and it did take the fall with dad for the social worker to get involved; possible it wouldn't have had it not happened but not sure.
All of dad's Aid and Attendance went to pay the caretaker, so there wasn't much involved to keep track of; they took care of everything else as part of their job. I'm not sure what Lindy's talking about re if you get your dad placed because I thought it would need/could be used to pay for that, if it had to be done, if he didn't qualify for Medicaid, which could easily be the case, that he could qualify for the A&A and not for Medicaid; the requirements are very different, but I don't see it being something your mom could qualify for if you place your dad, but then I'm not seeing that that's an issue anyway.
Regarding the A&A for senior vets: an individual vet, a vet and their spouse, or a surviving spouse may qualify for the benefit. I am not sure exactly how the VA figures their numbers, but it's worth looking into whether your mom might qualify for something too. It might just be that whatever time or money you are spending on her caregiving, medical expenses, etc. would be factored into the amount they decide to give them as a couple. It doesn't hurt to ask.