My husband and I each have two kids from our previous marriages. My children live with us full time, and my step-children go back and forth every other week to their Mom's, unless something comes up, then we rearrange a little. Their mom lives a mile away so it's easy to stay flexible.
I really like my husband's ex, and I feel she really likes me, we aren't exactly friends, but we appreciate and respect one another. We are complete opposites. She is an Ivy League graduate with a career in television journalism, who travels around the country doing motivational speeches. She is efficient, and exacting, and the kind of woman who follows a recipe. This year she completed her first marathon. I, on the other hand, am a high school drop out (I got my GED and went to college). I teach yoga part time, I measure almost nothing, and make up recipes as I go along. I run only for fun, and I never know how far, I just stop when I'm tired.
What we do have in common are these two kids. We both love them. We both want the best for them, and we are, together, "mothering" them. My step-son is older and is in college now. He's pretty much taken care of (other than reminding him to buy a ticket for a flight home on the holidays). My step-daughter is a high school junior, and is at an age where she needs a lot of guidance and intervention.
Because I only work part time, and I happen to work from home, I am usually the first person to see my step-daughter when she gets home from school. This is crunch time. This is when all of the maladies of the day come spilling out. I am the first "parent" who knows what's going on. I am frequently the one who answers the phone when my step-daughter left her homework in the printer. I am the one who can go to the pediatrician at the last minute. My husband and his ex-wife are committed, involved, loving parents. They are not pawning off their responsibilities on me, I just happen to be around.
Whenever a problem comes, up I either e-mail or call both my husband and his ex. I explain what's happened and what I think we should do. Sometimes they agree with me, and sometimes they don't. The hardest part is letting go of the decision making. Bottom line is, my husband and his ex-wife are the parents, even though I love my step-daughter, and I'm really involved, I have to respect their decisions.
Recently my step-daughter daughter had some trouble with her driving. My husband and I had a conversation and then I e-mailed back-and-forth with my husbands ex. Together we chose a course of action. I have to say, it was a great co-parenting experience. We came up with a plan, I think my step-daughter will benefit, and I felt heard, supported, and valued throughout the process. I hope my husband and his ex-wife felt the same way.
I once joked to my husband's ex wife that she is the closest thing I will ever have to a sister wife, she laughed and agreed.