Box fill calculation for isolated ground receptacles

After too much reading on what I thought would be straightforward, I'm a bit turned around on calculating box fill, and hoping I could get some help in doing so. Here is a diagram of the circuit: A few notes: Yellow lines are home runs for isolated grounds. Orange triangles are twist-caps, and I just grabbed a stock, non-IG outlet for the picture. All wire is 12awg stranded THWN run in LFMC or FMC, all boxes are metal, ideally for surface mount. Wiring in boxes B, C and D are the same as A, with one difference between each box – there is one less unbroken IG wire passing through the box compared to the one before it, so of course box D will have a smaller fill than A.

Thanks in advance!