I enjoyed this episode - an interesting family. I think Sebastian Coe came across as a bit uncomfortable - I'm not sure if this is solely due to the subject matter found, or whether he is just a bit nervous and camera shy.
I think in an hour long programme it would be impossible to cover all generations. There was plenty to just fill in this one line.
So although I would like to see research on other branches, it is probably better to just focus on one line and do it in more depth. In the intro they make a point of stating which line the celeb wants to trace, but I think this is probably staged, taking into account the most interesting and easily followed branch of the family.
What I do think could be really interesting is revisiting some of these personalities at a later date, to trace another branch/es, and also to see if the celeb has done further research of their own.