So much more going on here.................
There may have been no assets in either's estates that needed Probate.
There may be no assets.
Your brother may not have been provided for.
Your brother needs to take legal advice to see if he has any grounds/prospect to bring a Section 117 application.
Is your sister, who got the family home, the executor by any chance?
Has anyone approached the executor of either will?
Any chance of a family meeting? What ages are the surviving offspring? Any reason you can think of that brother not provided for?
mf