Mikaelsons + SO's
Well, like I just said to Kol, I reckon start at the beginning and keep on going. Gloss over the icky bits. Tell him you lot are immortal, gloss over the blood parts. Tell him you don't get along with your folks, try to skip the whole 'tried to kill us all' part.
Possibly avoid the whole sister being in hell part altogether and maybe skip the bit about one of his brothers shagging a male demon.
Failing that, act it all out with puppets. Everyone likes puppets, right?
Oh, and you might want to adjust the filter a tiny bit so he can't see it. Him being Mikaelson family and all.