Many issues can undermine a stepfamily marriage like disagreements about co-parenting, financial issues, or ongoing conflict between bitter ex-partners. If your marriage isn't unified these issues can divide you. So, to protect your marriage, communicate a lot. Resist blaming each other or letting your frustration spill out on the children. If co-parenting isn't going well, consult with a family mediator or therapist. And find a group of stepfamily couples at your church who can support you.