In a setup of having many Delver RMOSTC tasks in the same system, each Deliver database should contain unique Job definitions, and each task needs to have a separate and unique SYSID.
Even if the RMOSTC tasks go against the same job execution class or sysout class, the RMOSTC task with the lowest SYSID value will have the first opportunity at something matching that general criteria.
Next that would occur would be a review of the Job definitions within that particular Deliver database, to see if the job would be processed by that task.
If there is no match to the Job definitions, then it goes on to the next RMOSTC in the SYSID chain, to go through criteria, then it looks at the Job definitions there, and so on.
If there are RMOSTC tasks running on a different system, then you would need to ensure that the SYSID values are unique for that system, as they would need to be unique for the primary system.