none
the wills people BC and barmaid I am sure will be along in a mo
oops sorry to ask - is she the sole named executrix ?
BUT assuming you are joint executors as well:
you dont all have to apply for probate
you can and should on your own
Your dad's bank acct ( sorry for your loss and your half sister ) should have been frozen within a few days of his death and you should do so now - a death cert will do - then open an executors acct
This is a second matter however if dont want to employ a solicitor then the internet is full of do it yourself advice and so are we - a decent proportion have done it themselves
here is a start:
https://www.gov.uk/after-a-death/overview
Once you can show the acct has been operated after your dad's death - she presumably is the only person who could do so ( otherwise report it as theft ) then knock it off her inheritance and say you regard it as an advance
here is a starter for probate
https://www.gov.uk/wills-probate-inheritance/applying-for-a-grant-of-representation
by joint beneficiaries I conclude there is a will
even if there isnt you do the same sites but concentrate on the bits that say intestacy