I am still confused
"A mutli wire circuit with both branches off the same leg"
Article 100: Branch Circuit, Multiwire
makes clear that the hots are from different phases
If this is the case all #14s would be fine
But "with both branches off the same leg"
this would not be a multiwire branch circuit, it would be two hots of the same phase coming back on one neutral
the current would add up to potentially 30amps
never seen this done (On purpose) and my reaction would be that it is a violation,
But I do not know how to find it.
lighthouse we do this all the time with 4 wire 3H + 1N + 1G the advantages outway the problems for us.
And for the cables AFC will pretty much get whatever you need.
I just did a job using MC with 3 whites 2 greens 1 each black red blue all #10s Matched up to the office cube furniture
Construction & Maintenance Electrician