If you are flying Manchester to Boston In Business Class I don't think you are going to get much cheaper than £2635 for two people. Personally, I think that is a good deal. While calling the airline couldn't hurt, I would be shocked if they provided any sort of discount based on the description of your circumstances.

Have you considered purchasing 3 coach tickets? While you don't get the service with business class you will get the extra space, and probably cheaper.