Financing amount / rough realistic plan

We have been thinking about building a house within the next 2 years.

We have considered building a single-family house with a granny flat, in which my mother is supposed/wants to live in the foreseeable future.

We have now looked at several prefab house providers and find turnkey houses that meet our ideas between 250,000 and 350,000 thousand euros.
In addition, there would be a basement. (approx. 50,000 euros?)

We will not be able to pay for a plot where we currently live, so we are considering moving to a somewhat more rural area and are calculating with approximately 100,000 euros for land costs + incidental costs.

I am aware that this is a very rough plan and this is merely an initial "exploration," so 300,000 + 50,000 + 100,000 + at least 50,000 realistically puts us between 500,000 and 550,000 (right?)

Financial / family situation:

Income A: 2000 € net
Income B: 1800 € net
Equity: approximately 50,000

We are very economical with our living expenses:

( Rent currently 1100 €)
Additional housing costs: 250 €
Groceries: 250 €
Leisure: 100 €
Vacation: 50 €
Insurance: 20 €
Phone etc: 20 €

so all in all about 700 €

My mother would agree to pay 500 € monthly rent for the granny flat.
We calculate that we can additionally repay 1300 € monthly, so 1800 € monthly?

Family situation: We are planning 2 children in the not too distant future. Partner A will go back to work after parental leave (relatively secure situation with mother in the house). Salaries are also expected to increase somewhat; however, I would prefer not to plan with exact numbers here.

What else do we need to consider? Is the plan roughly realistic or completely exaggerated?
We are grateful for any help.

I wouldn't bet on a rate of 1800 €... what will you do if the mother goes into a nursing home in 10 years? Then they are out for the time being - a new tenant may take a few months to move in - although maybe it could still be done.

With 1300 € (but also with 1800€) you won't reach a loan amount of 500 T€ - but if you already have 100 T€ equity and maybe the house only costs 300 T€... 400 T€ loan amount would be borderline realistic.

In my opinion, costs and budget do not match here.

Costs may be correct, depending on location, house size, fittings, etc.... Are the €50k the additional costs? What about outdoor facilities, carport/garage, interior fittings (kitchen, furniture, etc.)? Due to lack of information, let's assume the costs roughly fit. Even if you calculate with the lower costs of €500k, you would have to finance €450k. That is simply too much with your salary.

I would also not necessarily include the mother's rent for the above reasons. Costs will definitely rise. Additional costs will be higher than what you have now. At the latest with a house and children, the costs for all the items you mentioned will be considerably higher than they are now. What is missing is the item "mobility" – car, monthly tickets, or similar. What about that – especially if you live in the countryside then? Children also "consume" quite a bit of money – keyword childcare – besides all the other things children need. What about clothing?

Die Gehälter werden sich voraussichtlich auch noch etwas nach oben korrigieren ich möchte hier aber ungern mit genauen Zahlen planen.

Unfortunately, the cost of living is also increasing. And will the salary increase exceed the additional costs with children and inflation?

If it absolutely has to be a home now, in my opinion you should scale back considerably. Does it have to be a new build or are there alternatives on the used property market? Could the house maybe be a bit smaller? Do you really need a basement? etc....

As the "previous speakers" have already pointed out, this does not quite fit together. In detail:

Income: Since 2 children are planned, equity A/2,000.- cannot be considered reliably achievable on a permanent basis, grandma or not. Rental income/mother depending on age and health condition is probably also not to be considered secure; while the granny flat could possibly be rented out to others, any additional effort due to home/care should be taken into account.

Cost of living: Very tightly calculated, especially when children come. You probably don't drive a car ?-)

If one assumes a financing requirement of 450k to 500k, it must be considered that banks at the current interest rate level and these equity ratios (with relatively low equity) demand higher repayments. One should assume interest + repayment of approx. 5% p.a., which amounts to EUR 22,500 to EUR 25,000 p.a. just to pay off the house.

Without further details, one can therefore only say: reduce the scope, reconsider the living conditions/plans, and calculate realistically (especially with regard to cost of living).