The sim uses only UDP traffic, so if the others using your Internet connection are using mostly TCP, and you can give priority to UDP traffic, that would be an easy first step.
There are two ends to each communication: the local end (your computer), and the server end (our server).
For the sim:
We use "ephemeral" ports on the local end. This means that your computer finds an unused port number, and uses it for its end of the connection. There is not much you will be able to do with that, since most programs do this same thing.
We use a fixed range of ports (15000..52500) on our race servers. Hopefully you can specify port ranges, and not just individual port numbers.
If you can give priority to (remote) IP address ranges, instead of port numbers, that would be more reliable.
126.96.36.199 and 188.8.131.52. Then 184.108.40.206 through 220.127.116.11.