PostDoc Discussion Forum

Hi all,
I'm currently in the process of looking for and applying to PhDs. I've found an advertised PhD project that I'm really interested in and I want to reach out to the supervisors for more information. However, there are 4 supervisors listed on this project - should I email all of them or just one of them? If I was going to email one of them, am I right to assume that the supervisor listed first is the lead supervisor? If it makes any difference the PhD is related to medicine/biological sciences.
Sorry if this is a silly question; I am a first generation student so this is all very new to me!