How can I make sure I am reimbursed from my father's estate as I make sacrifices to provide care and pay a large portion of his bills?

My father is 80 with Parkinson's and stage 4/5 cancer. He had a fall about two months ago and is now in hospice. He broke his hip, and he needs assistance in day to day living. He is also unprepared financially. There's no real timeline for anything but I had a horrible experience when my mother died and I hope I can do it better this time, if I set things up ahead of time.

I moved in about a year ago knowing he needed care and thinking I could reduce some of my bills. He was mostly mobile when I moved in, but he was starting to have issues. Gradually, I've had to take on more and more of his day-to-day tasks. Before this fall, I was doing laundry, keeping the house clean, and preparing all meals. If I didn't make dinner, he didn't eat! I was also paying him $1,000 a month and paying for all the groceries, internet, and outings like bowling once a week. He is a prideful man who lied to everyone about his health. Everyone thought he was okay when he was actually having falls weekly, couldn't always get dressed, and even spent an entire month at home in July when he got sick. Aside from the health problems, he doesn't have any real retirement income beyond social security. He would have lost his house to foreclosure without my financial help. Despite giving him "rent" and paying for most household expenses, he almost had his truck repossessed and there have been several foreclosure warnings posted.

Since the fall that broke his hip, he can't do anything for himself. I get him out of bed, dressed, fed, etc. He needs my help, I can give it, but I want to have something in writing that forces the estate to compensate me when this is done. When my mom died, I had to close down a successful business and give her 24/7 care. My full sister lived 40 minutes away, but she came down maybe 1-2 days per month. I ripped through my savings, paid for everything, and my sister didn't help with time or money. It wrecked me financially, emotionally, and physically... but I have no regrets. Caring for my mother is my proudest action in life.

My father is a slightly different situation. He owns the house I grew up in and has about 500k in equity. He cannot access the equity. That could be an entire post; please know that he cannot get a reverse mortgage or sell the house any time soon. I am giving him care. He can't afford to live in the house without my financial aid. He cannot live in the house without physical assistance too. The will is set up to split the estate evenly when he dies. I just want to get back the money I am paying him in rent. I don't care about being compensated for his care. I am finally healthy and have a good full-time job. I am spending more money living with him than I would if I moved out, not to mention my quality of life and free time would be unbelievable. I feel obligated to give him help and will probably do it no matter what, but there must be something I can do to at least be okay financially when this is all done! I deserve $1,000 per month back.

He is grateful for my help, both as a caretaker and with the money. He has said he would sign something that says I can get back the money I've given him. Right now, with the will splitting things equally among 7 heirs, it feels like I am giving my 6 siblings 85% of the money I spend on his house. I give him money, he pays the mortgage, the mortgage debt decreases my siblings' inheritances increase. They don't help him financially either. I don't want to keep spending money that is just going to my siblings, especially because they all live out of state (except the full sister who lives 30 minutes away from him) and nobody else can give their time.

What's the best way to get in writing that I will get back the "rent" I pay, before the estate is split equally 7 ways? Has anyone else managed to get some sort of agreement before the passing of their loved one, instead of feuding with family members after the death?