An additional aspect of the Three Sisters combination not mentioned in the other answer is that eating the combination of beans, corn, and squash provides a complete protein and a good balance of nutrients. I'm not certain, but I think your combination of sunflowers, peas, and squash might also provide this balance.
You could combine something tall like okra with a "bushy" cover like cabbage and a vining climber like peas. This would give you the cultural requirements: peas provide nitrogen to the okra, okra provides a support for the peas, and cabbage helps to choke out weeds. But while you'd get a decent shot of vitamins from eating the combination, you may not end up with a complete protein.