It seems to me that the extent to which B C D E will be able to get more money is to some extent dependent on their ability to plausibly precommit to rejecting an "unfair" deal... and possibly their ability to plausibly precommit to accepting a "fair" one.

Emphasis on "plausibly" and "PIRATES."

At minimum, if they can plausibly precommit to things, I'd expect at the very least CDE to precommit to tossing A B overboard no matter what is offered and splitting the pot three ways. There are quite possibly better commitments to make even than this.