What loan amount is realistic for house construction?

There seems to be a change regarding the maintenance obligation for relatives. Apparently, only the daughter / son will be considered with a limit of €100,000 annual gross income. Family income remains irrelevant.

Can anyone confirm this?

Perhaps it helps you that your girlfriend wants to become a co-owner.

Yes, something like that is planned, but it still needs to become law:

If the money of the person in need of care and the funds from the long-term care insurance are not sufficient, the children can be asked to pay for the services. However, in the future this will only be possible from an annual income of 100,000 euros gross. ...The threshold always applies per person with maintenance obligation, that is, per son or daughter of the person in need of care. Currently, the income limits are 21,600 euros net per year for singles and 38,800 euros net for families.

Even people with incomes over 100,000 euros will not face excessive burdens. Because the income of the spouse is no longer taken into account. In addition, they will still be able to claim high allowances, so that in the end their burden will usually amount to only a few hundred euros per month.

Source: Tagesschau

The OP wrote that the partner is not allowed to have any assets, which is already nonsense. The T€ 100 limit fits in positively here. The OP never told us why the partner is not allowed to become a co-owner.

When the limit comes and I really have to pay, I will go to the boss and switch to part-time. This injustice of people who deliver performance only being squeezed is no longer bearable.

Pure speculation, I suspect that the lady raised her hand... or is unsure with the partner and wants to be able to quickly get rid of the „tenant“.