Newsflash: Some advice on Rent to Own grandma’s house?

My fiance and I are late 20s in high COL area. His grandma was recently diagnosed with dementia and is going to be moving into a care facility around the end of the year. She wants us to buy her house and it’s very hard for her to fully part with it. But it brings her peace of mind to maybe help us buy when we wouldn’t necessarily be in the right position to do so otherwise. She wanted to carry the contract, but the complication arises from her children’s inheritance. Without being able to account for how long she will live & the cost of her care needs long term, we can’t be positive her savings can cover the money she’s promised her kids in her will. If it doesn’t, the remaining money owed will be coming from the sale of the house. 3/4 of her kids were okay with getting their inheritance segmented from our monthly payments, but 1 is not. She wants the lump sum when her mom passes as was promised. So we are scared to potentially go down this route and have to refinance at an indeterminate date when she passes and be in over our head with interest rates, property taxes, etc.So we’re looking into doing a rent to own option. This gives us the option to back out after Grandma passes if her savings don’t cover the inheritance and we wouldn’t be in the financial position to refinance. She wants it to be affordable, so she would be giving us a below market price on the house charging us around what our current monthly rent would be and have 50% towards principal. From my research it seems like most of the risks for the renter is 1) the unreliability of the seller, such as the ability to rescind the offer and pocketing all the principal if things fall through. 2) Us having to be responsible for major repairs.I’m not to worried about 1) because obviously Grandma wants this for us, so when we work with an attorney to write up the agreement it wouldn’t be the typical seller rent-to-own favored contract. It’d be purchase-option, give us the ability to purchase at any given time with adequate notice, etc. 2) If we had the contract carried as we originally preferred we would’ve been responsible for home repairs anyways. Property taxes are outrageous here and she would be covering that for us so I see that as a huge plus. Does this seem like a smart option? We make about 100k a year and have a small amount of student loan payments. We have about 30k in savings, and my fiance has the potential to ask his other grandpa for his inheritance early, around 20k. Both cars are paid off but I’ll need to buy a new car in the next 18 months. We are working to schedule an inspection and Grandma would potentially help with potential major repairs before we move in. If we do proceed, it’s probably best to put down as little as possible for a down payment right? As long as Grandma agrees to the amount.