It would be best if you didn't. One of the things the Court might look at were your brother to turn nasty is "suspicious circumstances". This may occur when someone draws up a Will for another person where they take significant benefit.
Assuming your father is worth only a few thousand in cash and assuming he has no spouse or children other than you and your brother the estate will automatically be divided between you and your brother under the intestacy rules so no need to bother.
If your family circumstances are different, post again.