I assumed that a family variable is just a shared variable among all objects... so it would just be updating that shared variable a bunch of times until it's the last object's z variable.
No, each object has it's own value. So you just put the z variable on the family instead of on the individual objects. Or if you give the family another var 'z2' like r0j0hound said, it will save you having to change your existing code.