Can i configure One MFR (e.g MFR1) with 3 subinterface(MFR1.1,1.2,1.3) to support 6 T1 Customer locations where 2 T1's belong to routerA, 2 T1 to routerB and 2 belong to routerC.

All 3 routers are located at different locations?

I will be using channelized T1's on 7613 and customers have 2821's

I have been told that it will not work unless all t1's belong to the same router, can someone confirm that?