Once you have got a copy of the will and the grant as BC says,
First of all you need to know if the ball park figures are out of kilter
try one more demand for the accounts - and then it looks as tho you are going to have to instruct a solicitor - and I dont say that often (at £200/h)
basically you are alleging breach of trust by the executors
which I agree could be dispelled in five minutes by the refused accounts
so you have to have at least some ammunition...
as usual we dont have all the facts - if you have got the proceeds of a house and not the house itself - then the selling price will be on zoopla and you can get an idea if you are not getting the full whack
if the executor is a solicitor - basically you are screwed - they can charge all sorts of things a sibling cant - which is a good reason NOT to have a lawyer as an exec of your will.
I have sympathy with you thug-you - a fren' was left a car as he found out when he got a copy of the will ( see BC's post) and as cool as cucumber the solicitor said to the fren' oh I have been told it is not available, it was given to charity three days after the fella died....
and he thought / hoped that was that ! (it wasnt)