Step-parenting can be a difficult task if the children are old enough to resent you and have strong ties with their other parent. Even if your partner has lost a spouse, the children may still remember enough about their mother or father that they don't want anyone to take his or her place. My daughter became a step-parent to two girls, four and eight. It took quite a while for the girls to love and respect her and as adults they greatly missed her after she died from breast cancer. Both of them told me how much she helped them and all the things she taught them that their own mother was too busy or uninterested to teach them. Jennifer had what she called her 1-800-Mom line that she used when she needed my help. It took quite a while for the children to follow her rules and realize she truly loved and cared about them. Now both are married and I am sure will use many of the things Jennifer taught them when they have children of their own.
Sometimes a step-parent finds that no matter what he or she does, there is just no way to make things better. Two step-mothers told me they finally had to get a divorce because each had a step-child who had their fathers completely under control. One step-son was a twenty-four-year old who slept on the couch, never looked for a job, and was probably using drugs. The step-mother finally gave up when her husband would not do anything about his son.
One sad case was a couple who were married in my garden and were much in love. Unfortunately, the woman had a very spoiled daughter who tried from day one to break up the marriage. It took her a year, but she succeeded. The couple are both dead now and I wonder what has happened to the girl and if she has any regrets?
Another woman told me she tried in every way she could to set limits for her step-daughter, but her husband would not back her up. The girl had two abortions and then after the couple were divorced decided to keep the baby after the third pregnancy. She relied on her former step-mother to help her and seemed to have matured quite a bit. So, all you can do is decide what yo will and will not accept and if the kids won't listen and your partner won't back you up, you have to make a choice about whether there is any future for your marriage.