It sounds like you have some way lost a generation in the database. I would first compact my database, and then print a simple generation report like an Outline report to see who is printed. You could also print one of the simple trees.
If there is indeed a problem, check the relationships of the people in the area of the problem People, Person, Relationship Tab. This will list three generation of the family and give you the ability to change the relationships if necessary.
Before I added anybody, I would search the People index to see if they are in the list.