League-of-legends – Is it possible to reroll champion shards into a champion I already own

The best option is to go premade with people you know.

If you solo then yes you should ask people what builds are they using and what lanes they want to be in,people will often be ok and tell you how they plan to play the game,but of course there are times when you just get people that want to troll and there is nothing you can do about it.

Personally what i sometimes do when i enter solo queue is that i type in:"STOP DON'T LOCK IN" as soon as i enter queue,and people often listen and do not lock it after that,and then i tell them that we should build our team carefully and most people are ok with that. Of course some people get rude about it and lock in with random champion and there is nothing you can do about them,either dodge queue or stick with them and hope for the best.

I would also mention that even if you get really weird team combination that you can still win if you're lucky.Even if your team may have crappy combination there is a chance that enemy team doesn't have good combination either or that they don't know how to play their champions so good.So there is always hope.

Rengar must kill or get an assist on and against Kha'Zix on the other team, just like Kha'Zix must kill or get an assist on and against Rengar of the other team. You could have the whole team be Rengars or Kha'Zix, but each one would have to get a kill/assist against the other team's opposite of them. Its per character, not global(Assuming the answer to that question is correct).