Stuart I totally understand your pickle. Nice that you've been able to come to a plan to do your dives. I'm more or less in the same situation, planning dives in the 70-110m range in the Mediterranean on the Ligurian coast(tirpitz passenger liner, u-455, etc) in 2 weeks. Last november I was there doing more or less same dives but we had a team of 4 people. 2 being OC (me and someone else), 1 being RB80 and 1 being JJccr (gue setup). Some dives we did split up (OC vs breathers) but some dives we did with 2 OC divers and an RB80 guy. No problem whatsoever with enough reserves within the team.
Problem now is that we'll be a team of 3 divers with me being the only OC diver. I obviously will carry enough gas to get both me and another diver to the next switch and enough deco gas to share at least one lost deco gas. Both breather divers will need to carry enough deco gas to share with me and their bottom gas (in case of RB80) or dilluent (in case of JJ) will need to be sufficient to carry me and them to next gas switch (in RB80 case) or next bailout (in JJ case). So we'll need to play with deep deco/travel gas to allow us more bottom time.
However mixing teams like this definitely is complicated and some procedures are difficult to align very well.