Trouble when build HVAC system with one room service 2 or more indoor unit ?

[Tien Duong]

with one room service by 2 or more Indoors units. for example, with FCU systems. I build in multiplex, I double or more same room if this room service with 2 or more FCU. And when I input OA in the room. with sum of OA. and then when autosize of fan in AHU units. With one room same in multiplex, I got double or more flow OA. Please give me advice when build system with one room service by 2 or more indoor unit.
Thank so much !