Is there not way to disable players in the same party from showing through walls? This happens even in FFA if the players join into a match from the same party. Name plates set to always hide.
Never found a solution to this, I believe it happens because when using Custom NPCs in order to make them agro to each other you need to assign them to different teams in the NPC definition. From what I see this ends up creating teams under the hood and causes players to be placed into teams as well even though the island settings are set to FFA. To fix this I use Verse to put the players onto team 1 as if it was setup for teams and enable friendly fire. This works but you end up with players in the same party being highlighted. There should be an option to not let players be visible like this, but it seems there is nothing that can really be done to stop it.