I propose that instead of having a bunch of combinations, perhaps allow members to select each segment individually. For say, having five categories, being "they, he, she", "them, him, her", "their, his, her", "theirs, his, hers", and "themself, himself, herself", but of course with many more options, and I propose that you allow members to select each individually, meaning one could have "they/it/their/its/themself", rather than either "they/them" or "it/it".

Thank you for your time,
  KingtheTitan