Put on a reasonable head and start discussions with your brother about what is known and common knowledge within the family.
Write down your fathers wishes about sharing and consider times when this was shared with others, what was his ethos on life and family,
Write down times he supported and helped his family to evidence his actions were family based.
Write down comments made by your mother about the future, when she spoke of any grand children and their future with others present.
What did she clearly infer and can be evidenced.
What did she know about everyone's financial situation.
What had she spent on anyone that she would consider part of their share. Had she paid off bills, made loans etc that she would consider as a pay off.
Did she treat everyone equally or was their any clear division.
How does each sibling view their position within the family.
Have you found out if the brother has been left everything or it has been left " to do as he feels best?"
My OH inherited all his fathers estate because the other siblings had been bailed out previously over the years. He knew no money would go to the grandchildren and he trusted OH to do the right thing.
Doesn't mean he didn't love them but in his mind he was leaving a level field. Did the other siblings view this in the same mind? No
It depends on your relationship with your brother and how well you can reason with him and get him to review good times and any continuing relation with you or other siblings.
Talking sensibly with him will get a quicker outcome than any court action. Your anger should not be aimed at him because this will ultimately backfire on you especially if you are incorrect about any pressure being brought to bear.
The will becomes a public document later on but he does not have to share it with you now. If he is lying it will come out later.
If I were him I would pass it over to a solicitor to deal with at @ 800. if there is a house transfer. He only needs to provide the solicitor with estimates of the estate and can then step back. The cost will come out of the estate as will the funeral costs. You may wish to negotiate something for your child if your relationship with your brother is fractured? He is their uncle and may be more inclined to put something aside for their future perhaps?
You are more likely to lose everything with your present attitude because I wouldn't wish to negotiate with any angry person making accusations about me. It does you no favours.
Step back, breathe deeply, write down what is known and can be evidenced and meditate. This is you best approach as court cases seldom go the other way.
When/ if you go to court not of the above suggestions are evidence.