Sorry, I didn't mean to down vote your comment.
I think we all know how to add parents, brothers, sisters, kids, etc... but some families (like mine) interconnect in a few places (small island problems). I need to know how to link siblings to people who are already on the family tree but were added after. Does that make sense? For example, my great great uncle is my brother's wife's great great great grandfather... I added them at separate times, and now I can't link them to each other.