The general statement, that the dead remain members of the lineage, is true of every tradition below and tells you almost nothing about any of them. The differences are where the doctrine actually lives.
Among the Igbo, the ndichie are the ancestors who died well, at a good age, and received full burial. Dying badly, by certain diseases or by suicide, or dying without descendants, disqualifies a person, and the disqualified dead are a danger rather than a resource. The ndichie are addressed at the family shrine and are understood to hold the lineage's ofo, the staff of authority, alongside its living elder.
Among the Akan, the nsamanfo are approached through the stool, a physical seat that is the lineage's continuity made into an object; a chief's blackened stool is his ancestral presence and is fed on the appointed days. The Adae cycle sets the calendar of that feeding.
Among the Zulu, the amadlozi or abaphansi, those below, remain in the homestead. They communicate through dreams and through illness, and a diviner is consulted to establish which ancestor is speaking and about what.
Among the Shona, the vadzimu are family ancestors and are distinguished from the mhondoro, the lion spirits of former chiefs whose concern is the land and rainfall for a whole territory rather than one household.
Among the Serer, the pangool merge ancestors with the spirits of particular places, so that an ancestor of standing can become the fangool of the ground the family holds.
Among the Yoruba, the egungun are met in masquerade: the ancestors return visibly, in costume, at fixed times, managed by a society constituted for the purpose.
Whether the ancestors are fed, argued with, danced, seated, or asked about the rain is not decoration on a shared belief. It is the belief.