Floor plan single-family house approx. 170m² - ideas wanted

what if you move your guest room or office to the upper floor and instead put the bedroom and shower bathroom in the basement?

That would definitely be an option. The idea to put the office in the basement came from the fact that I like it quieter when working. Since I work 100% from home (even after Corona), that is very important to me. If the office were on the upper floor – near the children's rooms – that would not always be the case. There would still be the spare room; I will think about how that could be arranged.

You can take the hobby room as "Your office," then hobby/guest upstairs. What kind of basement windows are planned on the side? The utility room could be divided into a shower bathroom and utility room...

Personally, I would not move the bedroom to the basement with small children. A whole floor in between and Child 1 is only 3 months old, Child 2 not yet born. That means many years of going up and down the stairs at night. Especially on the days when they are sick.

A whole floor in between and child 1 is only 3 months old, child 2 not yet born.

Well, you don't build a separate shower room for an unborn and an infant either.
As long as K2 doesn’t exist, there are two rooms free upstairs – just because they are labeled K2 and hobby/office doesn’t mean they are uninhabitable?...
A plan always shows the optimal use for four personality-forming human beings within a family, and the family formation isn’t even complete yet but still in flow?! So you’re allowed to use the rooms otherwise, right?