If the final restrictor is controlling all the storage, so that both CB structures form a level pool, then you could model them as a single "pond".  This will be easier to model (more stable) than attempting to model the equalizing effects between the two CB's.

Your "pond" can have a separate line in the storage table for each of the contributing volumes (above-grade, connecting pipe, CB, etc.)  In the outlet table, just list the restricting orifice.

What is a CB?

CAN A PRISMATOID CATCH BASIN HAVE TWO SEPARATE CULVERTS with different invert elevations,locations and sizes?

This would allow  controlling the outflow , both in magnitude and direction to different washes.

CB - Catch Basin

queque - Sure, you can have two outlets routed separately.  Set one to primary and the other to secondary.

I need two outlets. However , each outlet consists of a 18 in. culvert and a verticle orifice.
Which is primary and secondary?

i.e.  2 primaries and 2 secondaries?

I'd say to make the one with the higher invert your secondary.  Each outlet (primary & secondary) will have two components, the orifice and the pipe.  Make sure the orifice are routed through the pipes they are in.