x1 is a grandparent of x2 which/who has another grandparent x3 such that x1 is related to x2 by relationship x4, and x1 is related to x3 by relationship x5 which is NOT their mutual mating/intimate partnering, under cultural/personal paradigm x6; x1 and x3 are mutual co-grandparents.
x1 is a grandparent of x2 which/who has another grandparent x3 such that x1 is related to x2 by relationship x4, and x1 is related to x3 by mating/intimate partnering relationship x5, under cultural/personal paradigm(s) x6; x1 and x3 are mutually partnered co-grandparents.