If the two groups, in order to give Kivudim and honor their own relatives and close ones with a brocho, want to separate for the Birchas Hamazon, what should they do?

Poskim advice that in such a case, one of the Chasanim should temporarily leave the room while one set of brochos is recited. Once finished, he should reenter and have the second set of Sheva Brochos recited for him. Sovea Smochos (1: n. 150) mentions that Ponim Chadoshos or new invites may be required for the second set also. (See Hanesuim Kehilchosom 14: 92).