These two companions are pretty similar with their selection of epics that they can get.(However Bison Chief has one power that monquisitor doesn't have, and that's rouse. Also Bison Chief gets second chance as an option as well, while monquisitor doesn't.) Despite minor differences, they are still very similar with most of the epics they get, and the general role they play. But what build should I give them. Also, how do I play these two non relentless rank 2 wielding privateer companions?

There has to be some usefulness in them, right?

There's nothing redeemable about them. They are among the worst companions in the game. Not every companion is good and has a clear purpose. Some of them are just trash. In general, if a companion is not A) A storyline companion with dialogue (no, the ones that talk only when you recruit them, such as the bison don't count) B) A crown shop clone of a storyline companion (Temujin, Wu Tang, Pepe, Malik, etc) C) A unique side quest companion (Zeena is the only one in this category) D) Goronado, Nausica, or (maybe) Hoodoo Cornelius, that companion is not worth investing time and tomes to build and level it. Give them some talents that make them better at certain companion orders and send them off.