Collaborate, join forces, team up, ally, cooperate, combine efforts, conjoin, coact, merge, unite, work together, act jointly, form a partnership, pool resources, act in concert, coordinate, fuse, link up, band together, integrate, partner up, amalgamate. Expressions that can be used to convey the meaning of "be partners in" include "be in cahoots with," "be in league with," and "be hand in glove with." All of these alternatives indicate a shared goal or purpose that requires cooperation between individuals, groups, or organizations. They also imply a level of mutual trust and respect, and an understanding that success is best achieved through working together.