FWIW, a piece I wrote on the Hendreiki, to complement the Esvulari
overview in TT 12, will be out in a forthcoming UW. However, in the
mean time I would recommend TT 12 to you: as well as an Esvulari piece
by Greg and myself, it contains Simon Bray's excellent 'Caldvale
Manor', which is a really nice exploration of Esvulari/Hendreiki
relationships, drawn from our house campaign.
All the best
Mark