The team which is due to receive in the first game of a set shall decide
which player shall receive the first point in the game. Similarly, before the
second game starts, their opponents shall decide which player shall receive
the first point of that game. The player who was the receiver's partner for the first point of the game shall receive the second point and this rotation shall continue until the end of the game and the set.
After the receiver has returned the ball, either player in a team can hit
Case 1: Is one member of a doubles team allowed to play alone against
USTA Comment 15.1: Do the partners have to alternate making
shots during a rally? No. In the course of making a shot, only one
partner may hit the ball. If both of them hit the ball, either simultaneously
or consecutively, it is an illegal return. Mere clashing of
rackets does not make a return illegal unless it is clear that more
than one racket touched the ball.
USTA Comment 15.2: May a doubles team switch its receiving
order at the beginning of any set or Match Tiebreak? Yes. There is no
requirement that any doubles team retain the same receiving order
for a new set or Match Tiebreak.