Email to all potential supervisors listed on application
Yes, you should keep looking until you get a commitment. It would be unwise to delay. I'm sure the person you talked to isn't expecting you to ignore other possibilities or follow up on them. Otherwise you would have gotten an offer. 

Of course, you may be in a place where actual admission isn't in the hands of advisors, but a committee. In this case, no one can properly "accept" you until the larger institution does. So all offers in such places, from potential advisors, are tentative. Other places, the advisors accept and hire students, but even there, until you get a commitment, keep looking. 

Of course, you need to be honest, when asked, if you are following up other leads.  They will likely be aware, of course, since they know each other. This can't hurt you, and might even help. 

If you are in a position to visit the institution in person, you might consider doing that and speaking to some of these professors. Email is much less effective in this sort of thing.