When someone dies without a Will they are considered to have died �Intestate�.
There are strict rules over who should inherit the estate in these situations.
Firstly, the estate should go to any surviving married partner or civil partnership.
If there are no married partners or civil partners it follows a laid down hierarchy of distribution,
Children
Grandchildren
Parents of the deceased
Brothers & Sisters of the deceased
Nieces and Nephews
Anyone else
I suspect that your mum is administrating the estate as the children (who would inherit under intestacy rules) are not old enough to deal with these matters. However as administrator she is required to follow the law on division of the estate and without a Will to say who should get what she has to follow the intestacy requirements. She is not free to decide what she wants to do and should she not follow the law on this she could find herself open to action in the future if the children of your uncle find out they did not get what they are legally entitle to.
I suggest that your mum gets some legal advice on this (this can legitimately be deducted from eth residue of the estate (but she should keep careful records of how much she has spent and why).
This is also a very good reason why everyone over 18 should have a Will.