Adrial confirms your understanding, that Athabantian and Nibiru are closely related. Nibiru is a planetoid ship/station, comparable in size to a small planet or asteroid, and is composed of remains from Tiamat. Athabantian manifests in conjunction with Nibiru, yet vibrates at a higher frequency than Nibiru. You might say that their "spatial locations" overlap, and they are able to do this because they are in different dimensions.
(This post consolidates material that Adrial gave while answering questions from Vlad Kudin.)