Yes, it's not just a question about the father's will but his mother's will, isn't it?
So in 1997 father made a will. Two years later in 1999 his mother died leaving a will. Then in 2004 he remarried. When he remarried that was revoked - see what Freckle and I said below. So now he has no will. If he dies then the intestacy rules apply as to who gets what.
Those rules say
"Married person with children
Spouse gets everything up to £125,000 & personal possessions.
- Anything remaining is divided into two:-
o Half to the children at 18 or earlier marriage.
o Half in trust during spouse's lifetime - he or she gets the income. On spouse's death this half goes to the children.
If a child predeceases, leaving issue, his issue will take his share between them."
Your father now owns a house with his new wife which is probably in joint names so without a will that goes to her I think outside of the will as it's jointly held. Then what is left is divided as set out above.
Looking at what came from his mother - assuming your father's mother's husband is now dead, on her death your father got half her house. That is included in what he now leaves unless he got the cash and used it to buy his present house. Other 50% of mother's and her husband's house went to his chidlren. Seems a very simple will and your husband inherited under it.
You need to read again your father's and his mother's will - your father's might say if he remarries it isn't revoked and change the normal rules. If he really has no will now his new wife gets the house in joint names I think - their current home and £125,000 of his assets over and above that. If he has more than that it is divided as above - doesn't matter how he came by it - inheritance from his mother or whatever.