Spawn In End

(This needs to be multiplayer friendly)
I want to make it so when you join the world you spawn at 0 70 0 in the end dimension. Once you get the advancement Free the End your spawn should be in the overworld. Once one person has gotten the advancement Free the End, it should make a scoreboard go up by one. That way I can make it so when the scoreboard is one or above it gives everyone the Free the End advancement.
In this datapack the overworld is a void world except for an end portal, so it will have to be specific coordinates in the overworld (ex: -2 -64 0)