I think what my mom really wants is to go back her home 40+ years ago when she was taking care of her own mother and her aunt. She is constantly looking for them and worried that they need her and she can't find them.
I say to "go where the patient is in time" . Tell your mother that you will go over after a while and hope that she accepts that and stops fretting.
You can also tell her that a family member (that she will recognize the name) is with her mother and aunt right now and taking care of them.
Good luck with this. It is a difficult path to walk.
Reassure your mother that you arranged care for her own mother and aunt, and they are doing well. Then, ask for her help doing a chore or making a snack. Reassure and deflect. Your mother will continue to ask; stick to your story, whatever story works for her and for you.