Don’t disagree with any of what you posted and my wife and I have had many conversations covering these exact points. Unfortunately, these aren’t my parents, it’s my in-laws and, while well intentioned and very kind and generous, are the most passive aggressive people I know. It’s an odd family dynamic that none of the kids feel comfortable having frank conversations with their parents. My wife is the baby, by a lot (she was a later in life ooops!), and is treated as such by the rest of the family despite her being the most assertive member of the family. As far as additional heirs go, none of the kids have children and won’t ever have kids (probably a lot to unpack there that out of three children none had children of their own).
At some point if this issue doesn’t get worked out, the wife and I have discussed walking away from the house and letting her older sister just have it as she’s the only one of the three siblings that wants to hang on to it. It’s not worth it to us to create a tense family dynamic with her siblings. We’re already the black sheep of the family that don’t live in the PNW and don’t have a desire to do so.