Do we need another restriction?

[Oriental66]

My mum (died years ago)and stepdad( he died recently) have a declaration of trust. Stepsister is refusing to sell the house. There is a form A restriction as they were tenants in common.
She keeps asking me to remove mum's name!!
Is there a stronger restriction I can add as I am amazed at her vitriol and the lengths to which she is going. Thanks.
I would like to know how a conveyancer would look at it, too?

[Pezza54]

Have you got a copy of the declaration of trust?
Did your mum leave a will?
Likewise your stepdad?

What do the documents say about the property?