Hans-Werner Sinn expressed it quite aptly in an interview today. Initial instabilities are becoming apparent in the banks, which is why neither the FED nor the ECB will significantly raise interest rates any further. The fear of a banking crisis is far too great.
In this respect, I do not see the 10-year fixed interest rate as critical. With that income, it will work as long as the parent stays at home or goes part-time and earns less. As for grandma, one must always keep in mind that she will have to be cared for more or less intensively at some point. The day only has 24 hours and your jobs don’t exactly sound like the mentioned weekly working hours are sufficient... especially not if you want to pursue a career.
However, I would strike the gift from your mind. Too much can go wrong there. If your financing is based on that, it becomes dangerous. A serious argument, for whatever reason, and that’s the end of it. Or as already mentioned. Someone has to go to a nursing home, has an accident, suddenly gets the idea to buy a Porsche in their second youth, etc.