Weaving Plot Lines

This one is frustrating as it is very different from what I've done before if terms of structure

My female leads are clearly defined with their individual relationship story arcs.

What I am currently struggling with is blending them with a greater over reaching story arc that will develop the main crisis point. In some respects, it would be easier to seperate the stories but I don't want it that why. I want the characters to grow and act as support for each other forming a bond that only being thrust together in an unfamilar life can create. In short its the intereaction I want and I dont think there is enough for seperate stories.