In the physical world, we regard a person as a single entity with its own soul. In the spirit world however, its individuality is not separated in the same way. There are for example, affinities or counterparts of a group soul, and sometimes they incarnate at the same time.
The group-soul, or over-soul, is composed of a greater individuality. Fragments of this greater essence incarnate into this world for experiences that will add a luster to the greater part when they return to it. Only an infinitesimal part of the whole individuality can be manifested in physical form on Earth.
We do not lose our earthly individuality when we eventually connect with the group soul, for it is like a stream that flows into a river.