a 100mm at 6 ft distance won't really give a tight crop- I use a 150mm at about that distance (well - more like 7-8 ft, I tend to measure distances in "me"s, and that is about 1.2 me).
Is a RF precise enough at 6ft? Remember, you wanted shallow DOF...
Ah - two people, full figure? Ought to work, then. Could wish for a larger opening, though - Like the 150/3.5 (?) for ETRS.