Is financing a single-family house feasible for us?

It is slightly more than 300 sqm, but ultimately that doesn't really matter. The garage is a boundary construction, so the plan is feasible. The bank would have given us 100k more credit as well, which is why my wife sees everything extremely relaxed. Of course, I don't know if the bank cares if we can't afford the installment with children anymore. Through our equity and own contributions, the bank easily gets back its invested capital :-(

The bank does not include the non-existent children. However, you should do so.

Rightly so!

One more question, the architect friend who hopefully calculated the price for you: did he actually build single-family houses in recent years and is familiar with the current(!) prices in your area(!). If he usually only does civil engineering for large projects, works in the building authority or similar, I seriously doubt his price expertise for Southern Bavaria.

He didn’t calculate any prices for us at all; he only made the submission plan.
We are managing the construction supervision ourselves.
We also obtained quotes from the roof structure to the kitchen and added them up. We also have a buffer of 20k. But no idea if it will work out the way we imagine.

He didn't charge us any prices at all, he only made the input plan for us.
We are doing the construction management ourselves.
We also got quotes for everything from the roof frame to the kitchen and added them up. We have a 20k buffer as well. But no idea if it will work out the way we imagine.

And who is supervising all of that? You as civil servants?

I of course don't know if the bank doesn't care if we can no longer afford the installment with children.

Of course, they think you will decide if things get tight between selling the house and children or keeping the house and then without children. It's none of their business! Decisions are made based on current data and not on what you wish for. Please make sure to reflect on this point yourself! Is the party cellar possibly really more important than the second or third child?

We also got quotes from the roof structure to the kitchen and added them up. We also have a buffer of 20k. But no idea if it will work out as we imagine.

How detailed were the quotes? Did you have your architect review whether the volume and completeness fit? Also whether it is okay measured against your usual standards? "Construction costs: estimated 470k" Southern Bavaria practically doesn't go below 2500 Euro/m2 That is 400 TE for 160 m2 living space! Plus basement plus groundwork, let's say 80 TE. Plus 30 TE incidental costs are 510 TE. You can certainly save 40 TE through EL if the trades are available and can be coordinated in time (they also have family and main jobs!) But 20 TE for garden, 40 TE garage, 15 TE kitchen, 5 TE miscellaneous (mailbox, lights, small furniture etc.) are missing. 80 TE. So mathematically the basement! Oh yes, upgrades are of course missing. Plus construction manager and expert(s).

Our parents are supposed to take over the site management.
We also have plumbing and electrical in the form of our parents.
Since they are all retirees, there is also enough time available.

Our architect has not looked at the cost plan, so unfortunately surprises could occur :-(
At the current stage, we might actually find a second child less important than the basement.
Of course, that can change.

In an emergency, our parents could also step in, but that should of course only be seen as an absolute emergency and not if there is a 50 percent chance it will turn out that way.