Complex sentence: Many, once appointed, were ostracized by their fellow firefighters, so the model of a fraternal organization was used across the country in forming groups, most notably the Vulcan Society of the FDNY and the Stentorians of the LAFD, for them to join.
Split into simpler sentences: Many, once appointed, were ostracized by their fellow firefighters, so the model of a fraternal organization was used across the country in forming groups. The most notable of the groups were the Vulcan Society of the FDNY and the Stentorians of the LAFD for them to join.