Payments for a serviceman who is missing or captured

My relative is a serviceman, and I am worried that a situation may arise where he goes missing or is captured. I would like to clearly understand: in what specific cases can the family actually receive monetary support on his behalf, what documents need to be collected, and where should one apply first? I am also interested in whether it is mandatory to have a personal order from the serviceman, or if there is a procedure for the case if such an order is not available?