nova-compute spawns child processes, but not to run multiple
instances
of nova-compute itself.
Perhaps it's just something inaccurate with the process list where the
command part didn't get updated... not sure. In this case 6099 is the
normal parent nova-compute. The others are suspect.
Can you grab an strace log from them? Something like ...
# strace -p 5174 -o 5174.txt
Also do this, which might be more obvious if it's what we think it is:
ls -l /proc/5174/exe
--Dan