Is Wohn-Riester possible when moving in together? Experiences wanted

Hello dear community,

I will buy my grandmother’s house - she is still alive and lives in this house.
Part of my financing will probably be "Wohn-Riester" because I want/will move in myself.

Now it is such that I will probably use the house together with her as long as my grandmother is still alive. Without charge for her.

That shouldn’t actually be a problem regarding the assessment of my situation and the related payment of housing allowance, right?

Thanks in advance for your opinions and tips.
Best regards ~ Mario

Probably no problem. A phone call to DRV Bund, Zentrale Zulagenstelle helps. They gave us very kind and good advice. An alternative is a pension advisory office nearby, just google pension advice plus your location. Karsten