Wherever the Ipsos picked up our language, they may have also picked up on the bias of using the masculine form whenever gender is in doubt, and so since they couldn't fit their genders into the human pattern, they chose "brothers" instead of "sisters" or "siblings". Or the social role of these Ipsos may be parallel to the traditional social roles of males in our society so that's why they chose the masculine reference. Or they may have learned the other connotations of "brotherhood". Whatever the case is, I agree that since the Ipsos chose "brothers" to describe themselves, masculine pronouns are appropriate until we learn otherwise. At the same time, I don't think Zachary was wrong to refer to Caleb.s as "it." It would be very anthropocentric to assume that the Ipsos place the same degree of importance on gender identity that we do.
joule