The probate waiver signed is most likely just a waiver of notice of probate and not a waiver to give up any rights.
In order for your father to waive his rights to his inheritance, a letter stating that he is "I am writing to advise you that I am disclaiming my inheritance right to the _______ account of his son, (name and social security number) who died on (date)." Your father should then list the next of kin as determined under the following paragraph.
Under Ohio law, any funds would then pass as if your father predeceased your brother. Your father cannot select who gets the funds, they will pass under the intestacy statute if your brother did not leave a will. Money would go to your brother's mother if she is alive; otherwise, in equal shares to all of his siblings (if any sibling is no longer alive, that sibling's share will pass to that sibling's children).
After all this has been said, if your father is named as a beneficiary under your late brother's account and there is no contingent beneficiary
, the account will be paid over to the Estate
of (your late brother) and probate will need to be opened to obtain the funds.
I hope this has been helpful to you.