Should I Cold Email Prof+PHD/Grad Students for Research Co-Op

Hi I'm very desperate for a co-op still and I've been cold emailing professors to see if any of them are willing to take an unpaid undergrad.

I've been looking at some of the research groups and I was just wondering if it would be alright to email both the head prof and the grad students under them, or if I should just email the prof.

Thanks!