Thank you for your responses
My mother and father lived in the first property for numerous years. With the purchase of a second house, my father moved into it and lived there. They were still married; they just chose to live in different properties. The two properties were in both names.
I cannot think of a reason why the properties would not qualify for RNRBs. I don't know how far back her paperwork goes.
I've tried thinking about different possible negatives, for example, worried that gifting shares in her properties would leave her a tenant in common with her children. That it might reduce the total R/NRB available to her estate if her estate is reduced, but decided the total double R/NRB remains the same regardless of whether or not her estate is reduced, as she would still have retained ownership in the residential properties.
Regarding my brother's intentions for wanting my mother to gift parts of both properties to a child, I'd forgotten that he gave my father money towards purchasing the second house and spent lots of time refurbishing the property. Something that our other sibling didn't do. So, I think it is a case of I'll have a stake in the estate now. As for the retained non-gifted elements of both properties, he thinks our mother can pass on them on her own behalf and how she believes our father would have wanted her to do for their children. I suppose after the initial gifting of part of the properties, in her will, it's a clean slate, and the remainder is willed to us all in equal proportions.
Oh gosh, how we make our lives so complicated! instead of just living.
Once again thanks
Ps. not sure how my query ended up under the Stamp Duty Index