I think that's nonsense. I just talked with the rookies about the house for half an hour. Since then, no more. Apparently, the impression is that I constantly pressure and lecture them. I don’t even talk to them. Zero. Not a single word since then.
I find that attitude quite disrespectful, sorry. To me, it sounds like you think you know everything and the two can only do everything wrong. It makes me shudder with the mansard roof and also with the cottage (fits into the English countryside, but into a German new housing development???? Argh... just like those gorgeous Tuscan-style villas *shudders*). So, I’m definitely not on the same page as those two "rookies," but they are adults, they have their own ideas, and they have the right to do it that way. Since the budget is limited, I bet my head it will come down to some suitable standard floor plan from a well-known builder. But they are allowed to dream of something else first. Reality will definitely bring them down to earth soon enough.
Overall, I find it a bit presumptuous to already make floor plan drafts after having talked to the "rookies" for just half an hour. (Why do professional architects probably always need longer???)
Do they even want that? Will your suggestions be welcomed? Personally, I would probably forbid my uncle from doing that. Unless I know he really knows what he’s doing or I like his house so much that I ASK for support. Then it’s legitimate.
You say you’re doing this for fun. That’s fine. Do it because YOU enjoy it and it makes you happy to design something. But then there comes the next sentence, which personally annoys me:
What they do will be a surprise and then we’ll put everything on the table and stir it up vigorously.
Uh, WE will put everything on the table and stir it vigorously? Are you sure you are part of the decision-making process? Have they told you that, asked you? To me, that’s quite presumptuous again (maybe I’m a bit sensitive about that).
In the previous posts, I always get a bit of an arrogance vibe, as if "the rookies" have no clue and you want to present them with the ultimate solution.
My personal opinion: Let them do it, reality will painfully clip their wings soon enough. If they don’t explicitly ask you for help with the planning, I would hold back discreetly and wait to see what comes from them. If they appreciate your expertise, they will ask you. If it’s itching in your fingers to design something, then ask the two if you MAY support them (!!!), but accept if the answer is "no."
They are adults, they are building THEIR house and have a right to their mistakes and ideas. If they ask for support, great. But for me, this is turning into a farce (half an hour of talking, no one has asked the uncle for help so far, yet he’s already planning the niece’s house quite concretely because he thinks he knows better than the future homeowners, that really has potential for a comedy of errors, sorry!).
I think if it’s itching in your fingers, first ask if support is wanted. And then there should probably be a thorough conversation about what the ideas are, the budget, what absolutely has to be included, what not, etc. Listen to that without prejudice and then you can make your (surely well-intentioned) suggestions.
Oh, and one more thing:
My dad, for example, built his first house at 18. One corner didn’t quite end up 90 degrees when he was laying the bricks. He still has nightmares about it and it lowers the value of the house. That’s rubbish. Doesn’t have to be that way.
There is a difference between design errors and execution errors.