it seems implausible that nobody else has mentioned this, so perhaps it is a unique problem.
previous to the most recent build, accessing spellbooks and party companion inventory while at the defender’s heart was simple and intuitive. either the obvious is just beyond the grasp of this poor soul, or there is a bug at play because with the newest beta build, the only interactable character in defender’s heart is the main character, as well as the main’s animal companion.
maybe this is one of the numerous animal companion issues which has appeared in the new build? otherwise, it strains credulity that nobody else would have mentioned this curious new quirk.