[ATannahill]

This is what I think.

If you want to break up any potential alliance, go for it. If you are seated above teamA and teamB (both in top 8) go ahead and chose teamB, they can accept or deny, either way you prevented them from pairing up.

I don't know if they will ask you not to pick TeamB, but if they do politely tell them that that is not within your strategy. It is your right as an alliance captain to pick any team you want for any reason.