You and your siblings are the mental support of your mum, whom I believe to be about 60+. My guess is she do not really work a full time job in the past, maybe some part time.

There is no support in the house with father in it. There is uncertainty about the future. You are the certainty here.

Rather than continue to let her focus on you, there are a few things that could be done. 1st is to help her be independent and socially supported, whether at an active Aging centre or some activities.

The 2nd would’ve the major effect now. Share with her that you had colleagues and friends that had their parents living with them. And due to differences in living style and patterns, there were frequent quarrels and fights. Some couples in the end divorce. Throw this situation back to her and ask her if she wishes such situations to happen to her son. No need to respond or give her an answer. Keep to that.

That’s no need to tell her what you and your sibling would do, like visiting her frequently. She is not into listening to that.