Shattered Throne Checkpoints?

I know there are checkpoints but I don’t know where they are. I know there’s one after the labyrinth. When I die to Vorgeth, I respawn on the bit where you drop down to Vorgeth.

Is this a checkpoint?

If I get to a checkpoint, can my friends join in the fire team at that checkpoint if they haven’t actually done the bits previously. E.g. if I did the labyrinth and dropped down, can my friends join if they haven’t done the labyrinth this week yet and bypass the labyrinth because I’ve done it?