There are four of us siblings and we wanted to help our dad, to save him, to do anything... something. We got him through all the medical treatments, but the end was inevitable. Everyone had ideas that ranged from the desperate to the impossible, and dad resisted everything. It took us awhile to see that the problem wasn't him, but us. All our earnest efforts to help were driving him away and making him angry. He wasn't a child, and he did not want to be treated like invalid, but that's how our intervention made him feel. That was a harsh lesson to learn and we felt useless, but that was what our dad wanted.
Dad had a basic will, but like your mom, he hadn't made any end of life decisions and didn't want to talk about those issues. It would end up being our decision in the end, anyway, and we chose my brother who was closest to dad, to be the final arbiter if there was any disagreement, an arrangement that worked very well for us.
Dad didn't want our interference and our concerns only made him more upset. He was determined to do things his ways and he was content with his regular daily routine. We came to the realization that dad just wanted us to do the things he couldn't, so we did the little support services he allowed. We took turns doing a little house cleaning and his laundry. We cooked all the very unhealthy, but delicious meals he liked, delivered all plated and ready to heat up and he enjoyed all that. We kept him supplied with his favorite snacks because that's what he wanted, and all those little comforts made him happy.
We were heartbroken that he didn't want us to help him, and didn't want to discuss the things we felt were important. It was very hard onus kids, but we had to remember that it wasn't about us. Our dad was always a private man, the strong, silent type, and very independent, and he remained in charge the rest of his days.
I don't know if my experience is useful, but when it was all said and done, I know we did the right thing in letting our dad be his irascible, curmudgeonly old self. It's hard for any caregiver to get through the death of a loved one, so remember to take care of yourself. Let your own family in, they need you, and like yourself, they want to help and don't know how.
Peace to you and yours.