“brokered convention with 6 nominees”
Nope. Brokered convention with Rubio as Trump’s “choice” for VP.
Certainly delegates are not required to vote for the person who they were pledged to in most states after the first ballot. I suspect few of the delegates will be real Trump delegates. Instead they will be GOPe types who are attending based on winning caucus seats, who in many cases may have peferred some other candidate.
Candidates can try "throwing" their votes: For instance Rubio instructs "his" delegates to vote for Cruz, but the delegates are under no obligation to follow those instructions.
In most cases trying to "throw" the vote in the first round is technically against the rules, but it might happen. There are no legal penalties that I'm aware of for being an "unfaithful delegate".
How dedicated to candidates who have dropped out will their pledged delegates be. Say you are one of the handful of delegates that Carson picks up: do you feel a real duty to make a completely symbolic (and possibly rule-following) vote for Carson, or if you look at a convention in play do you decide "I'm going to help Ted Cruz" or "I'm going to help put Trump over the top so we don't have a brokered convention" or even: "I'm going to see what type of position I can get in the Rubio administration vs. the Cruz administration"?
"Brokered" implies some sort of order to the proceedings, but things are pretty different than the last time we went this route.