Whenever possible, it is best to make sure the children have met prior to the wedding. A wedding is a huge life changing event and to suddenly meet your new siblings at the wedding is a huge stress on all of the children involved. Even if the siblings to be live a continent away it is important to find a way that they can meet prior to the wedding.
If the soon to be new step parent, only has visiting alternate weekends, make sure to plan a few get together's prior to the wedding ceremony, so that the kids can become familiar with one another and get to know one another.
If both parties have full custody and all children will be living under the same roof, this is even more imperative.
More on this next week.