Hello....I just wanted to say hello and welcome to the board.
I am so sorry to hear about your senior boy...it is so difficult to watch our dogs age....very difficult.
I honestly do not have any advice other than trust your Vet and take his advice.
I do know that many times, seizures in elderly pets can be caused by a brain tumor.
Only good thoughts for your boy.
Hopefully, others can chime in for you that have more experience with seizures.