On the topic of sacrifice for Ace release, it's because the Whitebeard pirates rules. If you touch one of them they will come for you. The Marines are no exception. So it was a matter of principal. Either they did nothing and their own reputation and name would be hurt by it or they could do what they did now. Also Ace was a very loved one among the entire crew. The entire crew seems determined to lay down their lives if needed.

From a tactician's point of view it would have been better to sacrifice Ace to continue to be strong. But for a pirate crew that's like a family, saving Ace is the only choice that exist. I respect the Whitebeard crew for showing that they're not all talk and they not only enforce their rules against weaker pirates and marines like a bully, but also against those bigger then them self.