We have four sons. Grown now, but at the point we began thisvtransition, all were teens with the exception of the eldest. After the first BibFam Retreat
@KellyR and I sat down with the whole family on multiple successive nights to walk through the scriptures regarding headship and man as authority and leader. I took responsibility for not understanding and not fully teaching that role or its implications.
We walked through the lives of the patriarchs, etc and demonstrated from Scripture what we were learning. We had always taught that Scripture is true, so it was on that foundation we stood.
At that time, the boys said, 'yep, it's there. We don't want more wives, but we see it in Scripture.'
From then on, I pointed it out in Bible lessons often. I made it a point of conversation when appropriate. Kelly's journey was the harder one. The boys eventually picked it up as a fun/funny subtext to convesations and now fully accept the option for themselves and others. They've been to retreats, etc..
Keys: Admit you were wrong. What does Scripture say? Stand firmly together as husband and wife.
The older ones will have practical questions... talk through them and don't let the subject grow stale or get pushed to the backburner.