yup, been a step mom since I was 19 in both first and second marriage. It can be wonderful and it can be dreadful. Wonderful because you get free kids-not 1 minute of labor. I love my step daughters I cannot imagine my life without them.
but the down side is this: sometimes I feel sad because their Mom is their Mom. Its just that simple.
It is VERY important that you support their relationship with their biological mother. NEVER say an unpleasant word about their mother. You may have to stifle yourself because it is natural to have jealous or hard feelings toward her. I cannot emphasize enough the importance of this. You cannot let it suffice to hold back unkind words or actions toward their mother, you must actively support the relationship. This will be hard.
Get to know her and let her know that you will not try to undermine her in any way. I have done this in both my marriages and it works, if you are in her corner, she will be in yours. You are stuck with each other for life so make the most of it.
Let the kids know that you will not be used if they are mad at their mother. Kids are great but they will use.
If the kids ever give you a hard time, call their mother and get hints and suggestions. I am assuming it is a divorce situation.
Ask her what they like to eat, use her as a resource, make her your ally.
pm if you need advice, I've been at this a long time. My step kids range in age from 33 to 26.
Deb