Why on earth should you only show one salary to the bank?? According to your rule of thumb, the mentioned €5200 is enough for a €600,000 loan.
This crooked rule applied for low interest rates. Now it’s different. The bank will initially apply hefty high living cost allowances (inflation, energy) and then against that, a still sensible installment amount. €600,000 and €100,000 equity – gives you a pure installment at 2% repayment over 10 years of €2800. You will hardly/not get that through the bank with an income of €5200..
With high interest rates, 1% repayment is possible again. Then you’ll be done in about 40 years. With an inheritance in the background, I find an absolute minimum repayment acceptable.
The question to remains: How much is the bank willing to give you at most?
There will be an existing employment contract with a clearly defined end of the parental leave. And if that is not enough for the bank, then they will wait for the day when work is resumed again.
Because currently only one salary is available? Usually, banks do not accept promises like "I will resume with X again soon."
That is possible if you have it in writing. We had that with the first house as well. I had my employer prepare a document stating that I could resume with X hours from date X. The bank accepted that.