Sentence:  His parents talked seriously and lengthily to their own doctor and to a specialist at the University Hospital - Mr. McKinley was entitled to a discount for <WSD>members</WSD> of his family - and it was decided it would be best for him to take the remainder of the term off , spend a lot of time in bed and , for the rest , do pretty much as he chose - provided , of course , he chose to do nothing too exciting or too debilitating . 
Meaning of the word marked with <WSD> tags:  one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)