Many times the parent will want to put their children's needs before yours. Standing the background is a biological mother or father. She or he could have very strong feelings about you that have nothing to do with you as a person or stepparent. The biological parent could be jealous of your time with the children, fear your discipline, hate their ex, and distrust your motives. However unfair or unjustified these problems appear, you and your spouse have to deal them while trying to not get the children caught in the middle.
Child support is important.
Stepparents should not in anyway interfere with visits and child support responsibilities. It must be remembered by all, that parents are more likely to pay child support if they have an on going active relationship with their children. Remember most of the time the children didn't ask you to be there. You are intruding into their world, a place of familiarity and security. If you are having problems with the stepchildren, discuss these problems with your spouse privately, not within earshot of the children.