Hi Cordey
My love is with you at this hard time when your mum is very unwell.
I think the best thing to do is speak to a solicitor and get proper advice on where you might stand.
My other advice would be to try and keep this mix up from your mum as it's not worth upsetting her if she doesn't have long to go.
Try and sort it out with your brother and maybe ask the other siblings to help too.
And when the sad time comes, sort all the finance out after.
MY love to you and your family
xx