This is the name of the question: How do I have my PCs fight one another in an arena setting but then allow them to group up for the last encounter in the arena? [on hold]
I have added extra information but I do not see where this is alleviating the hold.
I'm one of the people that voted to close your question. @GreySage's comment on your question pretty much nails it, but I will elaborate.
Honestly, I think your question is awfully close to being off-topic for the site: it strikes me as an idea generation and discussion question ("Help me come up with ideas to do X"). To me, it seems like you're asking us to help plan your session in general. Stackexchange is better at addressing specific questions, and this one is pretty open-ended. We can tell you how to plan your session, but we can't do it for you.
In order to re-open your question, you need to present less, not more. The tooltip says,
Please clarify your specific problem or add additional details to highlight exactly what you need
The problem is that there are a lot of different questions inside your text. Here are a few:
Each one of these is more than enough to be a separate question on its own. I suspect that some of these are answered on this site somewhere, as well. You need to pick one of these questions and focus on it, rather than asking about how to do everything all at once. If you do need answers for all of those things, you can ask multiple questions, for which there is no penalty.
