Actually I am just as much interested in making the tree wider as I am in making it taller. I am just as much interested in identifying my more distant relations as my ancestors. After all, the people further out but within a few levels of me (the people that make the tree wide) are mostly still alive and are people that I see at family events and have no idea who they are. And, to learn who those unknown people are at family events is a large part of what started me on this project.
Of course, to make the tree wider, I've found it useful to start by going up the tree, then back down other branches. In other words: The grandparent level gives two families from which to trace offspring, going up to the great-grandparent level gives four families from which to trace offspring and find more distant relations, going up to the g-g-grandparent level gives eight families to trace down, and so on. Of course, the work level required also increases exponentially, too.
Of course, as just about anyone researching a family genealogy would do, I'm only looking up the bloodlines. While I will research my mother's father's family and my mother's mother's family, I won't research the family of the guy my maternal grandfather's sister married up, although I will trace it [/i]down[/i], because those people are blood relations.
Now, as far as adding the stepchildren I was asking about in the original post, here's the problem with actually putting them on the tree at all. Suppose I have a cousin "Ann" who is married to "Steve". Steve has kids from a previous marriage. If I enter these kids into the program I'm using, they will appear to be children of Ann and Steve--which they are not. The way around this is entering Steve's prior wife, then I can specify that those kids belong to that family, and not the family of Ann and Steve. So that means entering ex-spouses of people who are only on the tree at all because of marriage.