In the same vein as Adam Specker's answer, I think you are in a really rough situation here. The right answer really comes down to what kind of person your friends are.
You could, as Adam suggested, make an effort to play with them outside of the tournament. This might work, but there is also a chance that some of your friends will be a bit more spiteful. They might your efforts as a sign of pity, or they might be really offended that you think you're that much better than they are.
I really think the answer comes down to a few questions.
First, do your friends know that they are under-performing? If so that might make it easier.
Second, are you prepared to (in the worst case scenario) lose a friend or two, or at least be the group jerk for a few months? I'm sure they'll get over it in time, but yeah, some people might take it personally no matter what you say.
Lastly, and most importantly, do you value winning this tournament above spending time with your friends? Is it the winning that you enjoy, or is it playing with the people you like?
It's worth mentioning that I was in a similar situation a few months ago, but on the other side. I was in a minor E-Sports league, and it was pretty fun. I got to know some of the other players pretty well. I did under-perform a bit, though. At the end of the season, I was cut and replaced with someone who wasn't much better than me at all. It was annoying at first, but I knew that I wasn't doing great, and I accepted it. I still play with some of the people still on the team from time to time.
Long story short, they'll get over it. Or they won't, and you'll have found the friend not worth keeping. Someone who gets so spiteful over such a small thing is a dangerous friend to have. If you really want to get the gold, then your friends will probably understand. Just make sure the people you stock your team with live up to their reputation. You do not want to be put in the position of doing worse and having to tell your friends that you were wrong entirely.