There really isn't enough information there to provide any sort of meaningful advice. But, without knowing the full details of the situation two things spring to mind straight away. But, don't hold me to it as, I'm sure there are solicitors and others on this forum who specialise in probate and could offer more detailed and substantial advice than I can.
First, what was the position of the legal/equitable interest in the family home. Did your mother have any legal or equitable interest in the home? (Remember this is not automatic and up until relatively recently it was common practice to convey legal title into the sole name of the husband, therefore if the wife was to have any recognisable interest in the home it would be necessary to show either direct or indirect contribution to the purchase price, mortgage instalments or a general family fund). If she could not show either direct or indirect contributions then the husband would be deemed to be both legal and equitable owner of the property, in which case your mother would not have had any interest in the home to bequest in the first place.
Second, if she had a legal or equitable interest in the home then, what provisions were made in your mother's will to her husband(your father), if there were none or insufficient provisions then he would have been entitled to what is called the legal right share of her estate, which would have priority over other devises or bequests. s111(2) of the Succession Act 1965 provides: 'if the testator leaves a spouse and children, the spouse shall have a right to one-third of the estate'.
Essentially, what it comes down to is; a) whether your mother had a recognisable legal/equitable interest in the home in the first place, and; b) if she did have such an interest, what provisions were made for and did she make proper provision for the surviving spouse(i.e. at least one-third of her estate).