Sounds to me more like they enjoy remodeling and decorating houses (you say they’ve even “flipped” for profit), and they’re engaged in the intellectual and artistic exercise of “what if…”. Asking for details about the property as if they were going to buy and fix it is just part of the game. I do this myself all the time in similar contexts. Like a guy asking about another guy’s car, stereo or home theater set up.
It can be annoying if they’re throwing around ideas that you could never do for money reasons, but otherwise I’d take it as flattery that they really, really like your house and the “potential” it has.
If they’re your family though, and have “a frillion times more money than you do”, why don’t they just make a gift of some of these improvements or ideas to you some time? That’s what I would do in their place, if I loved my sister/daughter, loved her house, and thought I could convince her that, say, finishing her basement just so would be awesome. I’d pay for it to happen and see her happy and be happy seeing it done.
I’d probably tell them that those are very nice ideas, but that they should leave it alone because you aren’t interesed in selling anyway. Then ask them if they know that the housing market is crashing, and that the chances of them being able to sell the house again after doing lots of nice and expensive work to it are slim. So, by leaving you alone, they’re making you happy and by not buying your house, they’re saving themselves a lot of money.
And insulting because it’s telling you (the OP) that the way you have your house now is inadequate.
I had an ex-girlfriend who would do something similar only about personal appearance. She would talk openly about how good her sister would look if she lost 20 lbs and got a nose job. Lots of enthusiastic talk about wardrobe as if she was making some kind of future plans. “Yeah, and then you’d be able to wear such-and-such and you’d have a good wardrobe.”
It’s sort of like someone talking openly about how they would raise your children differently than you do. We all think it, because we all make different choices, but most of us think it inside.
This is typical behavior from someone who is primarily interested in his/her own world. There are a couple of words for it, all involv the root word “self.” They’re not thinking about what would make you happy, only about what would make them happy. So, ask them, “But what do you think *I * should do to improve *my * house? What do you think would make *me * happy?” If they don’t take the hint, follow **Mangetout’s ** advice.