This is a first attempt. Comments are welcome.
OK. Constructive criticism, hope it's taken as such.
1. I doubt you can connect the gates together directly, across phases, in the way you indicate.
Its possible of course this is intended as a "functional diagram" only, and you will in fact have three, isolated trigger circuits.
2. Connecting the 3 triac/scr groups like that, with resistors to a common point, I think will come back to haunt you.
Since you must have two (minimum) devices ON in order to conduct, I've doubts that you can actually trigger them while there's no potential across them. It would seem (to me) to be a far better arrangement to connect your loads in delta directly across the 3 phases (ie, one resistor/triac from A-B, another from B-C, and the last from C-A - that way, each will be directly between a phase.