I know this is going to sound bad,but I think if they are in a very good firm maybe making it uncomfortable for them at work can go a long way. Lawyers need to have their reputations especially in large firms . They are told to deal with personal problems and not let them come to the office. I think I would let them know you will make life uncomfortable if they don't compliy with the contract they signed. I also would put exact times and dates in a regestered letter so they can't say we did't receive any thing . I'd send it to their work that way who ever opens the mail knows too. I also would have all the other puppy owners make statements as to the condtion at the party. If you have pictures of all the dogs at the party get them to geather. I had this problem with a horse not a dog . I avodied court by all the above actions, The guy was worse he was a judge in our county.
Good luck Hope you can get good help from others.