Title: A Family's Portrait
Pairing: Hohenheim x Edward (not my particular flavor of pudding, but I'd never seen the pairing in doujinshi before and the art was too good to pass up). Implied Elricest.
Rating: R (sex, although not graphic and no nudity)
Warnings: Incest, sex, SPOILERS. This does take place after the last episode of the anime.
As for what's going on...I can only venture a guess. I really don't know most of the time, and if I tried to explain it I'd either make an ass of myself or go into spoiler territory, so if you are willing to give a post-series Hohenheim x Edward doujinshi a try, take a look. I tried to make the scans as nice as possible so that they could be used/scanlated.
Crossposted more places than I care to admit I am a member of.