You havent told us who was the residual beneficiary of your step dads will. Let us say it is Mr X ( can be more than one )
then from the facts, your mothers life tenancy has now ceased and the person who inherits is the one specified in your step dads will.
The law is clear on this. Your brother has ( on the facts you have given us ) no right to the house ( so long as his step dad excluded him or leftit to someone else ( like you ))
In terms of your mums estate - you inherit in equal proportions under the intestacy rules BUT if the accounts have been made joint then it is more complicated - they usually pass to the other joint-holder but if it were all your late mums property then you have a claim on it ( half to be exact ) as a result of this case:
http://www.fridaysmove.com/joint-bank-accounts-%E2%80%93-recent-case-re-northall-deceased-2010/15832
I dont often say this - you may need to see a solicitor
depends how serious your brother is