what is needed to "prove" we are blood relatives-

hello
We are "blood relatives" of our father-Army retired waren officer-(along with 3 brothers-1 army-2 air force)---our question is-how do we "prove" or Id needed to make reservations?

many thanks
the Mitchell's

I'm speculating that you are the adult children of a retired service member. Adult children generally do not have benefits such as commissary, exchange, health care or access to recreational facilities. Eligible children (used to be under the age of 18) need to get a military ID card and that is usually initiated by the retired service member.