4 level 1 players start in Limsa

[Iscah]

For example how can the 4 of us get into Sastasha with Marauder, Rogue and 2 DPS namely Arcanist which can change at level 30 Healer Scholar, or Summoner DPS. Sastasha starts at 15 but we wont have a healer in our 4 person group till level 30?

As a pre-formed party, the game will not require you to meet the standard party composition rules. You can go into dungeons with your tank-and-three-DPS setup and the arcanist still has Physick if you need it.