As Harrier Dude alluded to - you can pretty much expect that you'll be allowed to for an immediate family member (Mother, Father, Sister, Brother). Any extended family member, I wouldn't count on it. UNLESS they are In Loco Parentis ("In the Place of a Parent") that is, it's your grandmother/grandfather/aunt/uncle/etc... that raised you as if you were their son/daughter. Those are pretty much the rules in the fleet. They are more flexible when stateside (I've been given emergency leave for a grandparent), but when on deployment they are pretty hard and fast about them.