The kinship determination project is often the longest single piece in a BCG portfolio. Strictly speaking, it doesn't have to be. The specific requirements are to prove the two connections between three generations of the same family, and to place them in historical context. My second KDP was 71 pages long; a friend's was 13. We both passed.
The KDP can be deceptive, because we tend to identify it with the Complete Family History many of us aspire to write. In fact, a KDP doesn't have to encompass all of a family's children [NOT QUITE ACCURATE, FOR CORRECTION SEE JUDY RUSSELL'S FULL STATEMENT IN THE COMMENTS] and it doesn't have to contain all imaginable information about the family. (It is supposed to be a narrative -- in other words a story, and not a great pile of facts.) When you choose a family in your own direct line, however, the temptation to throw everything in is very great!
Another temptation is to put far more effort into it than into any other part of the portfolio, on the implicit assumption that it must be the most important item. But it's only just as important as any other.
Choosing a family for a KDP should not be as hard as some other choices. While we are required to connect generations, those proofs do not have to involve conflicting evidence (as does the case study). They do need to involve good-quality evidence of various kinds. This is the main thing the KDP has in common with the complex-evidence case study and even the client report: ideally they will all show off our skill at finding the relevant information, and analyzing and correlating different kinds of information from different kinds of records. That's what it's all about. Check out the work samples on the BCG site; just don't think that you have to do everything exactly the way those authors did it.
Harold Henderson, "Portfolio Choices for BCG Certification, Part 5 of 5: Kinship Determination Project," Midwestern Microhistory: A Genealogy Blog, posted 18 September 2012 (http://midwesternmicrohistory.blogspot.com : accessed [access date]). [Please feel free to link to the specific post if you prefer.]