So from the IMDB cast list and from lines/costumes in the film, we know this much is certain.
Noomi Rapace - Elizabeth Shaw
Michael Fassbender - David
Charlize Theron - Meredith Vickers
Idris Elba - Janek
Guy Pearce - Peter Weyland
Logan Marshall-Green - Charlie Holloway
Sean Harris - Fifield
Rafe Spall - Millburn
Emun Elliott - Chance
Benedict Wong - Ravel
Kate Dickie - Ford
Branwell Donaghey - Mercenary 1 (Jackson)
Vladimir 'Furdo' Furdik - Mercenary 2 (Vladimir)
C.C. Smiff - Mercenary 3 (Sheppard)
Shane Steyn - Mercenary 4 (Taplow)
James Embree - Mechanic 1 (
Florian Robin - Mechanic 2 (
Matthew Burgess - Mechanic 3 (
Eugene O'Hare - Mechanic 4 (Wallace)
The "Prometheus Wiki" and "Weyland Wiki" sites identify Mechanic 2 as "Barnes", and Mechanic 3 as "Ray".
Not sure how they confirmed whether Barnes was Embree's or Robin's character (process of elimination however rules out Burgess).
Also not sure where they got the name Ray from, although there was a mercenary by that name in the "Alien: Engineers" script.
I assume SD picked "Entragian" at random, which is fine, but I wish she'd been more decisive and paid more attention to detail, because she could have easily have clarified that Entragian was Burgess and at the same time picked a name for the other mystery mechanic.