I've seen people talk about it here and there, but I don't recall any specific threads where they talked about older kids.
What I have seen is you don't want to share specific details with them, but be as honest as you can as you don't want to lie to them either. Also reassure them this has nothing to do with them and they will be fine no matter what happens.
I'm sure your older boys have realized something is going on by now anyway, so its possible they know to some degree. Kids pick up on much more than we realize.
Accept what is, let go of what was, and have faith in what will be