As the DM, how do I handle enemy NPC Perception when the party approaches them without being stealthy?

I have a little question. My players are following a group of bandits, but the players are not hiding, they are even riding horses. They reach a beach where the 5 bandits are preparing a boat to retreat; 2 of the bandits are paying attention to see if someone comes, and the other 3 are just talking. My questions are:

  • The 3 Bandits talking use their passive perception to try to see the players, right?
  • The 2 Bandits that are paying attention roll for perception to see the players?
  • If my players doesn’t go in Hide, just riding the horses to the beach, whats the DC the bandits must roll?