Executor of a will may have stole money!

[baza...@excite.com]

I know the roll of duties of what the executor has to do when someone dies but in this case I feel they have not done what is needed. Hence some help.
My partners mother died last June 2015 and her niece were selected as the executor in 2005 when the will were wrote.
Her mum didn't have any property or land as she lived in a council house and the only bills she had were rent, gas, electric, water and phone. She didn't have any kind of debt at all.
She left the beneficiaries £22.000 in her will to be shared equally. After paying the bills and funeral they were left £12.000 to be shared between 8 beneficiaries? Now they all know that her bills and funeral cost don't amount to £10.000. The beneficiaries have been in touch with the executor to explain where the rest of the money as gone and all she said is "Leave me alone, that's the end of it" So basically, is that the end of it or can the beneficiaries do something about it without costing thousands as they have been told its not worth chasing up?
All help welcome.
Thanks