1. d20pfsrd is a useful website but it is not official, with the usual human error thrown in, (and 3PP mixed with official). Looking at old notes I have made trying to collate references over the last two years, (I do not own this item), I believe it is found in #28 The Infernal Syndrome and is a standalone, optional mini-system to enhance the possession abilities of stronger than average "fiends". The fact that the Feats can only be attributed to Evil Outsiders(?), that the system is an option for non-standard Monsters, (essentially homebrew/home game tweaked Monsters), and that none of these are actually used in the A.P.(?) seems to have resulted in it being treated as a suggestion rather than an "official" system - it is not on aonprd either, (which is the official reference site), not even under Optional Rule Systems. Paizo subsequently created the Magical Possession system under the Occult Rules, which presumably replaces the one that you are referencing.
2. The only reference on these forums that I could find is here, which does not really give any information beyond Possession Points relating to the attempting possessor's H.D. The author does provide an idea on how it works, however is unsure as it was altered in editing by others. This system (and relevant Feats) are not mentioned in the relevant G.M. Reference thread nor the wider Council of Thieves forum. Someone with the A.P. might be able to enlighten you though.