Will the last name be one of theirs cuz if so you could use the other grandpas name for the middle name so then you're honoring both, while still being fair to you. He should not get to just fully pick without your say.
I think dominika1980 and HanEli1980 are right...talk to her and then tell your husband thay before naming your son with their names he should ask about the type o fperson they were, what kin dof life they had etc, tell him to do some research!!! My sister wanted (if she had a boy but ended up a girl) to name her baby aftet my great grandfather but he did horrible things to 3 females my family when they were little so i knew the story i sat down and told her, you know you would really hurt the feelings of this 3 persons in our family if you name your baby like that and there is something you should know, so i explained everything and she understood!!! Just remember there might be someone in his family conected to that grandfather of his that will feel heartbroken if he/she finds out about the name even if its not the baby's fault i can cause bitter feelings,if that person wasn't good at all they will associate your babys name with that grandfather especially the hurted ones. I wish you good luck with that and i hope you can solve it.
His mother should never have told you that with the expectation that you'd keep it from him. I'd tell his mom that the truth needs to be revealed so he gets that name out of his head.
It's a hard one.
I personally believe in carrying names on through generations. If one day they ask - hey why am i called... I've got a pretty good story for them :) saying that, my first born was named after a character from a show we both religiously follow and we agreed on it immediately and without question. Still, there's a story we have in response to his question that is sure to come.
Speak to his mum. Maybe it's time he found out the truth about his grandfather. He's not a child and can handle it. I would hate to have my child named after a morally dubious individual.
Maybe tell him that you want the name to be equally special to both of you. If you can agree on a unique/special first name, maybe compromise on his middle name by honoring one of the grandfathers.
It should be equal. That's not fair at all.
My BF was the complete opposite cuz he didn't want to name any of his kids after anyone cuz he feels they should have their own names!