I could be wrong, but here's what I get from the whole Edda thing. She created or summoned those soul-less bodies for Avere to inhabit. However, he is too weak to inhabit those bodies. He needs a soul to absorb to make binding to one of those bodies possible. She summoned the Lalafell to Tam-tara to see if his soul was powerful enough. We don't know because we rescue him before Avere can possess? him. Now we enter. Edda's grand design was to get us to come in and use our souls to power Avere.

Ok, so we enter and do our thing. Could it have been a trial? See if our souls are powerful enough to handle everything that Tam-Tara throws at us? Edda even says we have strong souls to give Avere. Not entirely sure how this whole thing would play out if we failed. Would she have Avere eat our soul then possess the iron guys that we fight? Would he have possessed our soul and body?