My stepbrother might, just MIGHT be reasonable. He and my Mom speak on the phone weekly even though his Dad died years ago. My stepsister on the other hand is a wacko who has hated my Mom from day one cause her Dad married her within months of becoming a widower.
Both are extremely wealthly in their own right and don't need the money that the house would bring them. To them its pocket change.
What does that have to do with anything? Just seems to me this this only points to a class envy argument which nobody wins.
Why did your mother sign a pre-nup if she was not willing to live within the rules of it. This pre-nup did nothing but make second class citizens of you mom's family, and she knew and accepted that in a binding manner.
The argument that your mother "added" value to the house is also mute. Unfortunately that may be true on certain levels, but the argument that your mother held down values can also be made. Perhaps they would of remodeled the house and even further valued it can be made. The arguments that lost revenue due to reinvestment loses can be made. But, again those points are also mute since the owner (dead stepfather) contractually specifically that the house only be used to house your mom while she wanted to stay there. She could break the contract only one way, moving out now (or removing her items of value now before her death).
Signing contracts in this case prove that pre-nups are not always peace keepers that they seem at first glance. But also, the argument that perhaps this was the only way your stepfather could keep his house to pass down to his children can also be made.
Sin is why this life is so complex. In a perfect world, children would honor their parents, this family would be one instead of splintered, there would be no need for wills, no need for lawyers/courts, no need for pre-nups, and all love would be for each other and each other's wellbeing.
Yet naked we face the Lord as the day we were born.
I see an arbitrator in your future. You mom holds the keys now, she alone (in her old age where she should not have to deal with all this mess) can preserve the material items you want to inherit. IMHO...
I am not a lawyer, though I did once mediate a toy dispute between my kids (and I threw it away to cause less disputes in the future).