Single-family house approx. 180 m² - What do you think about that?

So somehow Yvonne adopted a new language over the weekend. I don't understand a thing. What do you mean by 1.2 WC? What is a space-saving RH? And what is "Schiddern"?

1.20 wide
Space-saving terraced house
Schiddern = to shit

Guest toilet with 120 cm width for the WC I no longer call RH standard, I rather see 90 cm there.

Our guest toilet is 1.30m wide and feels rather spacious for a guest toilet only

I really enjoy going to the sauna and savor it, but honestly: how often do you get to go? Once a week? Maybe twice in winter, less often in summer. With three kids, rather less often...
Giving the sauna the best location and the living room in the second row? And the bedroom is completely disadvantaged. How often do you lie in the bedroom, how many hours per day, how often are you in the sauna, how many hours per day?
How often do you sit in the living room, how often in the sauna?
I understand that you want to create a nice wellness area, but always keep in mind how often you realistically use it. And definitely incorporate that into the planning.
I would really start over, or consult a good architect.

our guest toilet is 1.30m wide and feels rather spacious for a purely guest toilet

Spacious? We have 1.20m and I hate our architect for that... I would never do it that way again. I think it is very hard to judge how big/small such measurements are beforehand. On the plan it still looked spacious, now in the shell with all the pipes, which will still be covered, I find it too tight. Let's see how it looks when the sanitary fixtures are in, maybe my opinion will change and I will find it spacious... but I seriously doubt it...

I just checked my notes again, the toilet is actually 1.39 meters wide and 2 meters long. The washing machine was originally supposed to fit in there, but the door is too narrow and I never wanted a top loader again. Of course, I can't fit a cabinet in there (except under the sink, which didn't get a pre-wall installation because of the poorly fitting door, rental apartment :/ ) and since we have no window, it's a bit dark, but I don't find it cramped at all. Actually, those 20 cm probably make a big difference. So, okay, it is rather narrow, but I really don't think you need much more. In our guest toilet, we have wasted space; I would have preferred the extra 10-20 cm in the adjacent kitchen. So I can't use it for anything since there was no room left for a cabinet.