Is financing feasible this way? Are the fixed costs okay or too high?

Your costs are already understandable. The rent is quite decent, the 620€ for the BAföG also hit hard, but they will pass. You spend quite a lot of money on telecommunications. Apparently, expensive smartphones were cross-subsidized. After 24 months, you could halve that if you continued to use the existing device. Cars would be cheaper if you finished financing and kept them for more than four years. Always wanting to drive new cars has its price. Insurances are reasonable so far. You explained the high photovoltaic cost, that it has an additional module, and the item for household contents/etc. is probably mainly high because of legal protection insurance, I would assume. Without this, the insurances could easily be had for half the price. You are used to high rent. When the BAföG installment is freed up, the monthly burden already looks very good. "Only" the equity is still missing. Regarding the topic "promotional house," I advise waiting a bit until the winter clearance sale begins; then the real bargains come SCNR

We already live in a semi-detached house, so the rent is relatively high. You are right about the phones. One of them still has the phone attached. But that is not set in stone for decades. So far, this is the first round with the cars. They get 1000 km added each time from some trips to our parents, plus 2x50 km for the commute to work and back. It definitely has to be the case that you can rely on the cars. But as I said, the issue with the cars is being dealt with promptly.

Currently we have a financing offer over 30 years with two KfW loans as well as an owner loan and an annuity loan, which is secured by a home savings contract.

KfW is fixed for 20 years

How does that work? 124 is only max 10. With 153, it is 20.

There's already a gap...

our rent with €1116 is very high

Why?

Because 1633 + house additional costs are around €2000.

Quite a figure

And with children, it's really something else

How big will the house actually be?

It will be 137 sqm. No, that is the current cold rent. The warm rent is just under €1300.

We have the small and the large KFW loan, the small one will be replaced after 10 years by a building society contract, which will be paid off after another 10 years. Therefore, interest is fixed for 20 years. With the large KFW loan, we still have to refinance €30,000 after 20 years. Everything else is secured or paid.