Seeking expert counseling is a sign of strength. A personal relationship with a caring professional is proven clinically effective.
I believe that I can help with this issue.
Family problems often arise when greed lifts its sorrowful head, particular at times of final transitions.
It seems that sibling relations are already compromised by your younger sister's manipulations.
You cannot change your sister's behaviour, particularly if she is a sociopath (implying narcissistic personality disorder with a need to dominate, manipulate, rule, control others through deception and lies and false outward presentation, all the while having no real empathy for the feelings of others).
The best you can do is to insert yourselves into the picture and use your own influence with your mother so as to disallow your sister from completely taking over and changing the will.
You are advised to talk with a solicitor about preventing the change by declaring your mother incompetent to change the will, if she is indeed incompetent.
f would like to direct you to a book about narcissistic personality disorder that can help you understand how to deal with these individuals.
I cant talk to a solicitor as mum's will is with public trust who wont discuss anything with me even though I tried.
Let me find he book for you then which will help you deal with and understand your sister.
I cant discuss with a solicitor as mums will is with public trust who wont involve me.