Batting first in the 45-over-a-side affair, Brothers scored 207 for five with former Indian Test all-rounder Sanjeev Sharma hammering an unbeaten 54. Opener Shezan scored 35 while Jahangir and Sanwar chipped in with 28 runs each.
In reply, Biman were restricted to 195 for nine.
National skipper Aminul Islam was not out 47 and his captain Faruque Ahmed made a run-a-ball 30.
Brothers' off-spinner Sanwar captured three wickets.
Another friendly match will be played today between Surjo Tarun and Victoria Sporting Club.