Okay, I normal team up to knock out the weekly challenges as fast as I can. And for the last few weeks I would finish some PVE challenges in Custom Firefight, but when I took friends into the same custom game, they do not get any count towards their challenges. So after finishing this weeks PVE challenges in it with a friend. I finished my challenges but they did not. When we looked they didn’t have anything count towards theirs that game. So we switched leadership in the game and played the same game and they got everything that time.
So only the Leader of the group gets anything counted to the challenges in Custom games. I’m not sure if the challenges where meant to be like that but I found it odd to have it that way. Maybe its a glitch in the code, or not. Who knows.