Historian of Chabad and hasidut Schneur Zalman Alpert writes:
… By and large most of the great grand children of the Tzemach Tzedek were modern people and their children were no longer religious. The same process occurred with the Chasidim themselves. Except for Lubavitch, the other branches of Chabad died out as the children of the Rebbes refused to take on leadership of a mystical nature and remained either Rabbis or in most cases lay people.
In all of Lubavitch today there is only one Schneerson family (a father and 2 married sons) who are frum and Chabad. Most [Orthodox] descendants of the Alter Rebbe in Chabad today are from a line that immigrated to Palestine in the early 19th century not the Schneersohn family that remained in Russia.…
One can also add that the 1st Chabad rebbe's son Moshe converted to Christianity and that today Chabad is hemorrhaging – by many estimates it is losing as many Chabad Jews to non-observance as it is attracting new adherents.
Read Schneur Zalman Alpert's entire comment here.