My mother made a will and in her will she left her share of the house to me and my two brothers .and my dad did the same 10years ago my mum passed away so her half of the house was left to me and my 2 brothers my eldest brother being executor .since then my father has died but unbeknown to me changed his will disregarded my mums will and left the entire estate to my eldest brother I have contacted my brother but he is saying he is unaware of my mums will but I know this will exists but he says it doesn't where do I stand

IF what you say is true, your father cannot have left the entire house to your oldest brother. It was part yours when your mother died.
But I have a feeling that the story isn't quite right. You would have received your share 10 years ago, and known it. Perhaps your mother left it to your dad, which is the most common arrangement between spouses.
You and your other brother should talk to a lawyer about both wills. If your mother's estate was never probated, then it's possible that her will was ignored.
I have a feeling that you are in the UK?