I've heard of people playing court rules where the two players on the same side in doubles play sides rather than alternate shots. Is this legal and if so what are the rules please.
As the IITF rules state:
2.8.2 In doubles, except as provided in 2.8.3, the server shall first make a service, the receiver shall then make a return, the partner of the server shall then make a return, the partner of the receiver shall then make a return and thereafter each player in turn in that sequence shall make a return.
2.8.3 In doubles, when at least one player of a pair is in a wheelchair due to a physical disability, the server shall first make a service, the receiver shall then make a return but thereafter either player of the disabled pair may make returns.
In the official rules, there is no such thing as court rule. The only exception to taking alternate shots is when players are in wheelchairs.