You may use multiple loops i.e. each loop for one port communication.
PS: I used to have one similar program talking to four ports i.e. 4x uPs. Queue event structure may be used.
There are many ways to achieve that.
Attached example of two loops is just one of many ways. You may rename the VI and modify it to suit your needs i.e. adding more loops.
PS: Sorry that it is not appropriate/ inconvenient to give you the actual codes of the 4-ports independent communications with uPs.