Need some help please

My mother has recently died, she has a will and my sister is the executor but I'm concerned at what has happened since the funeral. My sister has moved into mums home and made my brother homeless, she has took many of mums possessions included monies in her 3 accounts, also my other sister has taken all mums jewellery and thousands in cash that was in mums house.
All this has happened before the 6 siblings have seen/read the will so I would appreciate any advice on what I should do now.

Thanks Philip, UK.