Step Families Support Group
Traditionally, a stepfamily is the family one acquires when a parent enters a new marriage, whether the parent was widowed or divorced. This community is focused on many of the relationships and issues that may arise within stepfamilies where you may find answers from some members and you may help other members with their questions.
I would try talking to their step-mom first being as that she's already made contact and she may feel less threatened (and less drama) if you go to her first.
Kudos to you for being your children's advocate but realize there is just so much you can do; do it and then let it go.
Good luck!
In my H's custody decree, my SD could stop visiting her BM @ a certain age if she chose but until then, my H could not interfere with their visitations. If it's not being too personal, what are the rules that you have to abide by? I think Rfrew is right in talking to both SM and BD but you may not be able to change things.
and a 6-4 13-yr old?? Heavens, woman-he still has growing to do.