Some models are asked to pose nude with other people.  As in the
case of photography sessions, the situation should be arranged ahead
of time, and may be refused, even then.  At the very least, models
must be compatible with each other, and the qualifications they
require for posing with someone else (what age or what sex a partner
should be, for example), needs to be respected and accepted.

Posing nude with someone else is basically an intimate experience,
if it is meaningful at all, and must have advance preparation on the
part of willing models.  Each pose requires mutual agreement on the
part of the models; the most practical way of working this out is with
models who are already thoroughly comfortable with each other.
Intimate poses bv people who are thoroughly comfortable with each other
are very deeply moving, to models as well as to artists, and can inspire
wonderful works of art.