Bridge or interim financing

Hello everyone, I am new to this forum and have already looked for my topic but nothing really fits, so now this thread.
the following situation:
I live with my wife and daughter in our own single-family house built in 1900, bought and renovated in 2000 for 140,000. 100% financing back then, current balance 110,000 repayment 860€ monthly at 5.6%
my parents-in-law have now transferred their house to us and we first want to convert everything on the ground floor to be age-appropriate for them and then renovate the 1st floor and move in there so that we can take care of the elderly in case of emergency.
So far so good, the house currently lived in should then be sold. But how can I get money from the bank for the renovation of the new home while simultaneously servicing the old loan? I hope to generate the entire outstanding amount through the sale, but what if not? I have cautiously estimated the renovation costs at 50-70,000 €, but I still need a cushion as I have to pay out two siblings and, to top it all off, the building is still under [Denkmalschutz].
So now I am open to constructive financing ideas and look forward to every serious piece of advice regarding the financing of this whole mess.

Regards

Lepo

Many heartfelt thanks for the flood of constructive suggestions. This is such a suuper lively forum here.

Then here is a first constructive suggestion: Just go to your local bank and ask. In the end, that is where you will get your money (or not, if it doesn’t fit). Otherwise, more information about your question is needed: - Rent payment by the parents - Securing the renovation financing (are land charges possible or is there a restriction of the right of residence in Section II?) - Why are you moving into an apartment (at this point in time) and giving up a single-family home - Are costs or the possible selling price of your house already determined - Has the sale of the house already been initiated, etc. Unfortunately, constructive suggestions without any information do not work...