Taking Over Grandparents House, How Should I Approach Agreement?

[Jerry Villa]

TLDR: What agreement should I write between my grandmother and I so I can take over her house (mortgage payment, agree to buy the house at a predetermined cost), while we keep in her name and then finance/buy it at a later time?

Long story:

I recently posted that my grandfather passed away this month, coincidentally happening right when I was pulling the trigger on next steps into proper real estate investment. My grandmother is still with us but she wont be able to live alone in their house, the place needs a lot of work. I've done the BRRR calculations and it makes sense for a lot of reasons (sentimental and financially) that I should take over the place. I've talked it over with the the family (uncles, parents, and grandmother) and it looks like we're going to keep the house in my grandmothers name while I move forward with the house. So, we'll be agreeing to a fair price on the property in the condition its in. The house wouldn't be able to be sold on retail market in the shape its in and really can only be sold to investors. The amount we're thinking its worth though will probably equal the loan amount, so she doesn't have any equity really. I would need to put in $25k-$40k of rehab into the place (ac, roof, gas, and much more). At a later time, either in a couple of months, a year, or whatever is best, I'm planning to get a loan to buy the place out right, the ARV should give me room to pay the first mortgage off (value her and i agreed to), rehab cost (either another loan or credit cards), and give me some equity to use for another project later on (BRRR strategy). My question are the following:

1. What sort of agreement should I create this week with on the purchase price?
2. When should I plan to actually BUY the house from her, should I do it soon, a year, or keep it in her name as long as possible (her mortgage is low, she pays no/little property taxes, etc)? What are the cons of keeping it in her name?
3. Lets say the purchase prices is the same as the amount she owes her bank, can we just make an agreement that says we'll pay the bank whatever the pay off is when I do choose to buy? Because if I buy in a month, I would have paid one mortgage payment, if in 1yr I would have paid down the mortgage 12 payments, etc
4. Should I worry if she passes away suddenly and it goes to probate, should I do anything else or add something in an agreement to cover that?

We're looking for something simple to understand but still covers things. I don't expect any problems later on, but want to make sure if she ever has issues with memory or decisions that she doesn't change her mind in a couple of months after I've put in $30k of rehabbing or any other family members coming to start issues.