If you and Jean have a strong relationship, shouldn't it be able to survive you bringing up something unconventional and maybe even a little threatening, as long as you let her know that you love her and that she's your first priority, and that if she's open to considering the idea then you'll go slow and act with respect and honesty?
Just talk to her first, let her know you haven't said a word to Danny and won't until you and she have reached some sort of agreement. You've gotta start with trust. Find some good essays you like that she could read. www.MoreThanTwo.com
is a great resource for that.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.