Building a house - building savings contract with bad interest rates

monthly savings amount currently + your cold rent - some security, that would be your possible rate.

How much money do you save monthly and how much does your apartment cost you currently? The more precise the information is, the easier it is. Then it depends on how secure your job is. The advantage is you still have over 30 years until retirement, so quite a bit is possible...

Since we do not know your income, you should first visit your house bank to find out how much credit they will grant you. Even if you can increase your equity through donations (we are not talking about 10 or 20,000 euros here), repaying the loan can become very difficult for you if the salary does not correspond to the desired amount.

Just saying

aber wir wollen es unbedingt haben...

does not work permanently in life.

Relatives are not only there to be milked!

So cold rent 635, 285 euros additional costs, 80€ electricity. We also save almost 200€ additionally. It's just annoying, I'm still on parental leave but not for much longer.

Yes, that's true...
Regarding our work situation: I will be working full-time again, 40 hours, starting in March. The employer will not go bankrupt or anything like that, and we both also have permanent contracts...

Additional costs remain, 900 as repayment is not much. 200000 can probably be financed with it, but the current interest rates favor others more here.

I have the impression that I read somewhere that parental leave is also supposed to come up again??

well, that should at least be enough for a rate of 600 - 700€.

That corresponds to a remaining debt of 82,000€ at the end with a loan of 200,000€ at 2.5% over 25 years.
If you work again and special repayments are possible, then this amount works. But where do the other 175,000€ come from?