Separate names with a comma.
You can spectate players on 1 v 1 arenas, 2 v 2, 3 v 3 etc... too. And if you want to record a hacker there's a kit which have invisibility...
I think that should be more arenas, not at FFA, I mean on 1 v 1 arenas, should have more arenas, and bigger arenas.
Of course, if you haven't challenged someone, and then you type /accept, obviously will give you an error because there's no one who you have...
Look at your kit, maybe it has a high level of speed effect.