Welcome to the FortNite early access adventures of husk slaying. I’m sure you probably want to play with a friend and they may be on PC or Xbox One. Good news is that it IS possible to party with them and play together!
You just need to cheese a few things to get it to work: (Quite simple)
1.) Both players need to be friends via the general epic games account.
2.) The PC player is actually able to see them appear on their friend list when they are in game.
3.) Party invites wont go through but, If the PC player clicks on the top right friends menu, they can click on the Xbox One players name and click join party.
From here you can swap party leader and each player can invite from their perspective system. (PS4 to Xbox One and PC to PC)