"We worked/collaborated with professors and PhD students from XYZ university" should suffice. "Group of people" is too general; it could mean anybody from that university. It would be even better if you could mention what kind of professors you worked with, with regards to their fields of research. This applies when referring to PhD students too.
Also, it sounds like you're talking about research of some sort that involves professors and PhD students from a university. Try referring to each of them individually, with respect to the specific work that they contributed to your collaboration with them.