Before I begin, the circumstances surrounding this situation have not fully fleshed themselves out yet, but the ball certainly is in motion. I've been a spectator thus far but I fear I eventually may be pulled into this and will need to have an opinion.
Backstory: My wife's side of the family owns a lakefront property and has owned it since before the area was even a lake. It's the oldest and most prime piece of property on the entire lake and the whole area is on the rise. The number of properties on the lake has more than doubled in the past 5 years. The lake house is large and well-maintained (has enough space to comfortably sleep 20+ people for an entire summer) and is co-owned by my wife's mom, her siblings, and their dad. The property is appraised at $500k, but market value is almost triple that. Generations of family have grown up spending months on the lake and at times, members of the family (including my mother in law for the 3 years after my wife was born) have made it their permanent residence.
Issue: Nobody, save for my In-Laws (including my wife, myself, and our son) uses the lake house anymore. Extensive renovations were done a few years back and the cost was split evenly, but most of the family has been to the property once or twice since then to see it. Most of the family lives 12+ hours away and their lives take them to more affluent areas to vacation. There has been talk for a while of selling the house and splitting the profits equally (even though the family hardly uses it, insurance and utilities are split evenly among the family). Lately, these conversations have been happening more frequently and it looks like this may be an eventuality.
My in-laws spend probably about a month's worth of time there (it's 4 hours away, so long weekends are spent in the summer). My wife and her mom get very, very, very emotional at the thought of seeing the house go. My in-laws are looking at buying out the rest of the family and owning the house outright. I could go into greater detail, but the bottom line is that you could fill a book with their justifications for keeping the house.
Where I need advice: My in laws would essentially have to re-mortgage their house to buy out the family. They have asked to do so at the appraised value, not the market value. They could not afford the market value. There is little I could do or would do to dissuade them from doing this. HOWEVER - it was recently implied that down the road for my wife and her siblings (for us, this would start immediately), the upkeep of the house would be a shared responsibility. This would derail my plans for FIRE for a few years but my wife seems adamant that the house stays in the family. She wants to see our son grow up there. For a myriad of reasons, renting is an unlikely proposition, nor is listing it on VRBO or AirBnB. I can elaborate if necessary.
How would you broach this subject? How do I say that I don't want to incur the responsibility of upkeep without sounding ungrateful?