Sure, there is.
For retro PvP, for example, no Matter if you are guild or in party, you can kill them without taking anykind of skull.
For open PvP, in orden to be able to attack a member of your pt/guild, you need to have opened situation on the same player; for example if you open pk/yellow on a player, you Will attack other player that also have, until this player is killed, lose situation, or relog into the Game.