Financing without equity - Repayment / Interest

The funding and expenses + reserves for the current house are included in these issues at the moment.

In these expenses, the financing and expenses + reserves for the current house are included.

How much of the expenses specifically go to the current house?

Unfortunately, I can relate to this topic. However, background information does not belong here and is also irrelevant.

I would say... I think the part of the care costs for rent can certainly be included in the calculation. But the larger part of it and the child benefit have no place in it. Since the care allowance is only available for a limited period, I would only finance up to that point. Anything else I consider morally reprehensible.

Then you would also have to deduct the costs that arise from the care of the 3 children.

how much of the expenses go specifically to the current house?

Installment, electricity, gas, water, sewage, garbage, property tax, chimney sweep, household contents, liability, building/fire, 2x risk insurance, and reserve for repairs (that's why no equity, because in September we have to do windows) Total rounded: €1670

Regarding your existing property, you could also try to include a clause in the sales contract that allows you to remain living in the house for X months after the contract is signed. It is also possible that you will have an amount X (e.g., 1,000 euros rent x 9 months) deducted from the purchase price. How feasible such a sale with this clause is and to what extent a "rent deduction" applies depends on the real estate demand in your region.
Advantage: You save yourself the hassle of searching for an apartment, a complete interim move, and you know the "rent" incurred in the meantime. Furthermore, you can present the sales proceeds to the bank.
Accordingly, you should of course be at the stage in your planning where, upon signing the contract, you immediately secure the land and construction can begin.
Be sure to clarify with the bank before the sale how and under what conditions a loan repayment is possible.