Either the cold rent of the apartment is set far too low or the value is set far too high. Currently, the value would be at 44 annual rents, which is set way too high given the current interest rates. What else does "sale not yet possible" mean? Speculation tax? If you live in it yourself, then only a 2-year period applies.
Then the question remains how many children there should be and what the two individual incomes look like. Costs should be calculated with children if they are firmly planned – I would say it could be tight with 2.5k.
Otherwise, theoretically, you seem to be able to cover most of the costs from equity, so...