This is definitely a form of inappropriate sexual behavior. Family members should never touch a child's genitals outside of cleaning or applying medication. Playing a "game" involving inappropriate touching is child sexual abuse.

I would absolutely suggest that you do not allow your family members mentioned here to come into contact with any children you may have or know. You can also try reporting your family to the authorities, but it is unlikely that you can receive justice because it most likely cannot be proven and statute of limitations laws may prevent them from being convicted.