House purchase - Is our planning working?!

Hello, we have been looking for a two-family house (for us and my parents) for some time. The bank has already given us the green light for the project, but I am always extremely critical with such matters and prefer to ask twice. We currently have a house in sight: - 180 sqm living space, of which 65 sqm are intended as a separate apartment for my parents - purchase price would be 377,000 euros (roughly 422,000 euros including incidental costs) - the roof and basement would need to be insulated As equity, we have a newly built condominium with an underground parking space, which was estimated at 200,000 euros by the Sparkasse. Another advisor suggested the figure of 250,000 euros. In addition, there would be roughly 30,000 euros from the savings book. Monthly, we currently have 1,700 euros net (both full-time) left over after all fixed costs. From my parents, we would receive roughly 600 euros in rent plus ancillary costs. I would like to consider all costs for the entire house, as my parents could not pay more monthly. Do you think the whole project is realistic so that the property would be paid off in 25-30 years? And what if children come along in the near future? I have already calculated everything multiple times (modernization, half salary, job loss, etc.)... In my opinion, it would work, and yet I am still unsure. What is your opinion on this?

I always tell myself: from 4000, a lot is possible. With rental income, you are there, but if a child comes, then you are back in the crisis zone... Are you okay with 115sqm?

115sqm would probably be enough for us. At the moment, all of this would probably still be manageable, but this point "what if there are children in the near future and I possibly only work part-time" just won't leave my mind. We could probably still save here and there, but I don't want to get to the point where I have to count every cent three times or where the debt counselor is standing at the door in 15 years...

Rental income... not rental income...

Calculate the scenario for yourself when you are on parental leave. Then the parental benefits will be added later... overall, you cannot avoid a cost statement.
Basically a profit and loss statement

If I were on parental leave, that would be roughly 700 euros less per month, but then 150 euros in [Kindergeld] would be added. So 550 euros less....

I am roughly offsetting the monthly expenses for the child with what I would save monthly on fuel and food in the canteen.

For ancillary costs, roughly 500-600 euros would probably be incurred for the house?!

That means:
1700+600-550=1750 for installments, ancillary costs, and some savings

Would that be correct?

On the internet, there are these free mortgage calculators. I have calculated the worst and best case with them. Does that roughly fit?

The bank offered us a monthly rate between 600-800 euros without problems, whereby the 6XX was calculated with 1.5% repayment. I don’t want to start at 1% and later find out that the rates cannot be minimized or that we still have a remaining debt of 100,000 after the fixed interest period.

Otherwise, a longer term would also be worth considering...