Yes legally you are correct. The mother legally did inherit the home and has no obligation to share any of that windfall with her adult children. The grandparents didn’t put in any legal requirements that the house not be sold/scammed away from in a reverse mortgage scheme.
My point wasn’t about the legality of the situation just refuting the implied point from the original replay, that while OP did nothing to be entitled to an inheritance, neither did their mother.
Pulling up the ladder on your way up is a generally shitty thing to do.