You can. -insert lenny face- not hard. If they invite you to a fireteam, you join, you replace your own spot in the strike. If that makes sense to you.[spoiler]I doubt it.[/spoiler] From there you can kick whomever you like. [spoiler]like that guy who just sat and danced for a whole heroic when he was 310, who I invited, and messaged saying I'd carry a few more. I proceeded to kick him from the fireteam and finish it and listened to the insuing rage.[/spoiler]