@Former-Member ..... I found your answer so comprehensive .... I think it says everything I would like to say, except perhaps this ....
I have a daughter with an intellectual, and some physical disabilities who is in her mid-20's. I have been a carer for her long before my hubby's mi defined itself as disturbingly as it did. This has thrown me into being the carer for all my family, and the worst of it when they won't do the simple things I need from them to keep the household operational .... the most simple basic things, and circumstantial depr session seems to leave them leaden .... add my D2 being bright enough to be fully attitudinal and jealous of her siblings abilities, and it's frustrating to its core ....
One of my solutions to the emotional quagmire has been to stop and imagine that I were a paid carer for all of these people whom I love, and it can actually change your focus quite dramatically. As an "employee of the household", I have the right to remain far more emotionally neutral and objective in terms of everyone's behaviour. It helps you to switch into the sort of mind set you have dealing with the "terrible two's" stage of babysitting someone else's 2yo .... they are ultimately not your responsibility beyond taking all reasonable precaution to keep them safe, and offer opportunity to keep them cheerful if they will engage .... otherwise it's just getting on with the job in all other aspects and not expecting miracles.
That is not intended to sound patronising .... rather simply pragmatic .... a 2yo is defined by their immaturity and you need to respect that .... a disability or mi has its own limitations and boundaries which may or may not be transitional or temporary.
An employee has th commission to remain polite under all circumstances, and this, in my experience, is the ultimate shield .... if you apply the self-commison of being as polite as you can towards the one you are caring for, again, it can relieve the emotional responsibility of accepting bad or uncaring behaviours in them.
I hope that makes sense, and I hope it helps ....