If the house is owned as joint tenants that will automatically become hers, so anything left to you will have to come from his sole assets, a lot will depend on how the Will is written. Did he have £100k of his own? If you are the first beneficiary in the Will you will get everything up to the £100k before other beneficiaries receive theirs. If your stepmother is first beneficiary of certain amount or items, then you will get what is left up to max £100k, if less your share will be reduced.
Probate is required if sole assests exceed £5000, and Banks and Insurance Companies cannot pay out without probate being produced, once a Will has gone to Probate it is open for anyone to see and you will be able to get a copy.
With Insurance policies they can be written into Trust to keep them out of the Estate, and will be paid out direct to the Trustee, or they are assigned to a Mortgage Company in order to pay of any Mortgage without going through the Estate.