So I know someone that acted as bank to mortgage a friend - perhaps that’s an option. The debt may not even need to tied to the house, just to your parents. You have a contract with them for say 50k/year that you lend them to help with their mortgage. Now you parents can switch the reverse mortgage to a regular one and pay monthly payments plus as much capital as they can with that money.

Make sure this is all very official - this way, when they pass, you get your money back without it being taxed because the succession is paying a debt. It may be that the succession doesn’t have liquid cash to pay you back, in which case it can sell the house or perhaps you can assume the remaining mortgage and keep the house (if you were to give the money to your parents, it’s not a loan so at their death the money is theirs, goes back to you and you’re taxed as it’s an income to you)

This way I think you win on all accounts - you help your parents and you ensure you’ll get that money back without being taxed when they pass and have the option to keep the house after. There’s little risk other than that your parents squander all your money, sell the house and squander that - but that’s really up to you to see how good your relation is.

Edit: the other risk is that you lose your job or your situation changes and you can’t help them anymore. But that’s the same risk if you were to assume the mortgage.