Maithanet was of the Few, as Proyas and Akka discuss in TDTCB.
Maithanet probably did not have children, since his credibility as a religious leader would be compromised if he did, and that would interfere with his mission. Note however that it seems only to be Inrithi priests that must be celibate, the subordinate cults of the Hundred seems to have at least some hereditary priests in them (e.g. the High Cultist of Gilgaol).