Specifying cores for different applications Mac studio M1 Ultra

[Mrlipsham]

I've been running different blender instances using the Automator and running the shell command to open up blender in multiple instances. My issue is the CPU usage does not increase when rendering on multiple instances at once and the rendering is slow. I'm assuming this is because they're all sharing the same cores. I'm using eevee render engine but I get the same issue with cycles.

How can I assign separate cores to separate application instances, or any other solution if I'm getting this wrong?

Thanks, any solution or help greatly appreciated!