WHEN YOU PLAY A VARSITY SPORT IN HIGH SCHOOL you have to juggle a lot of balls in the air. Just ask Concord-Carlisle All-Scholastic soccer players Mike and Andrea O'Brien. In addition to leading their teams into the MIAA's postseason, the brother-sister act have something else in common: All-America recognition. Two All-Americans under one roof. Now, at the end of Fall, the Globe and Boston.com toasts the O'Briens, along with athletes from Barnstable to Georgetown, all of whom earned All-Scholastics honors.