How to find PID of all processes related to a given process?

How can I go about finding the PID or other information about a process that is doing the work of another process? I'm talking about

threads, for example, or any other threads/processes that are doing work within the kernel for another process. My dilemma is that I have a real-time scheduled process

(SCHED_FIFO)

running at sched prio 99, with CPU affinity bound to CPU 0, but when I inject CPU stress onto my machine, I notice that my important rt process is not able to preempt the other, non-important processes. I'm thinking this may be because the

that do work for this important process do not inherit the priority that the main process has, even though I specify the -a option in taskset and chrt. My current idea is to manually taskset and chrt the kworker threads so they don't get preempted by other, non-rt processes.