Complex sentence: They are very few groups that hold to the use of the Sacred Name: the only unified group, exclusively using the Sacred Name (Yahweh) being the Assemblies of Yahweh which has existed for nearly half a century.
Split into simpler sentences: They are very few groups that hold to the use of the Sacred Name. The only unified group exclusively using the Sacred Name "Yahweh" being the Assemblies of Yahweh, which has existed for nearly half a century.