I think you would need to pick your ship based on "assigning" a portion of the scu to each member for effectiveness. Lets say a certain commodity would have a profit of 1k per scu, and your team wants to each make 50k per run. Assume player 1 has one ship with 120 scu and one with 50, and player 2 has one with 50. Combined the small ships have 100 scu, so they could team up and crew the 120 scu ship for a 20% increase in scu capacity as whole, assuming costs are split 50/50. They could increase their risk by flying the 120 and the 50 together, but obviously there would be a higher chance of losses.

You could scale that up, assigning say 60 scu per member to make a decent profit off the target commodity, a 3 person team would want a 180 scu ship at minimum, or 3 60 scu ships flying together for safety. 4 would be 240 etc..