Thank you both for your replies.
Bronte, we asked the solicitor would it be a case that Marys share should go to her children, and she said no, that the portion of the estate left to Mary would be treated as if my uncle died intestate.
As my uncle has 6 siblings (3 alive, 3 dead) she says that the quarter, would be divided by 6, 3 already named beneficiaries get 1/6 each and the children of the 3 deceased would get their respective 1/6 divided amongst them...
So Marys two children will get 1/6 of the quarter, divided in two, according to the solicitor????!!!