Empire of Sin

Playing as Maxim Zelnick (the DLC character), simply save, hire the two gangsters of your choosing, and then re-load once the achievement pops.

While this isn't an exhaustive list, the pairings I identified for this achievement were:

Hugh Miller (#10 Brown final row) & Gibby Willard (#7 Green 2nd last row)
Guido Cervone (#8 Brown final row) & Bernie Barners (#8 Purple 2nd row)
Norah Quinn (#5 Brown final row) & Josephine Doody (#8 Blue 3rd row)
Ma Miller (#3 Brown final row) & Gertrud Brandt (#1 Green 4th row)
Boris Petrov (#5 Green 4th row) & The Cleaner (#3 Gold 1st row)
Esther Milotti (#2 Blue 3rd row) & Gail Grady (#4 Blue 3rd row)
Percival Lancaster (#5 Blue 3rd row) & Alfred Westcott (#3 Purple 2nd row)
Jack Mcgurn (#6 Blue 3rd row) & George Moran (#1 Purple 2nd row)
Man Running (#12 Green 3rd row) & Elsie Williams (#4 Gold 1st row)
Ray Monks (#10 Purple 2nd row) & Dale Mahan (#7) or Bruno Baldini (#5 Purple 2nd row)
Bernie Barnes (#8 Purple 2nd row) & Elsie Williams (#4 Gold 1st row)
George Moran (#1 Purple 2nd row) & Frank Nitti (#12 Purple 1st row)
Ada Santos Souza (#11 Purple 1st row) & Dixie Chan (#5 Gold 1st row)
Marco Behrmann (#9 Gold 1st row) & Dotty Bacon (#7 Gold 1st row)
The Cleaner (#3 Gold 1st row) & R (#1 Gold 1st row)

Hope this helps. There are some gangster pairings you normally wouldn't be able to use that Maxim Zelnick's ability makes possible.