Having an heir would presumably have increased Ezar's perceived suitability for the succession. Lurking in the background until the other candidates have mostly destroyed each other has resulted in more than one unlikely historical ruler. Also, making a marital alliance with whoever else survives and assumes power, instead of having to defend a pre-existing extended family of in-laws, could be advantageous. Perhaps there were multiple strategic reasons for him to wait.

There's a family tree on the wiki but I can't verify it:

http://vorkosigan.wikia.com/wiki/Vorbarra

http://vignette3.wikia.nocookie.net/vorkosigan/images/6/6d/Vorbarra.gif/revision/latest?cb=20081227101225