Wow that sounds terrible- sorry you're dealing with that! Have your letter writers actually said that they don't have the time to look over your materials, or are they just failing to respond? I know a few people whose letter writers fell under the "absent-minded professor" category, so they had to continue reminding them to stay on schedule with everything. But I can't imagine that professors who thought highly enough of you to write your letters would be unwilling to look over your application. If they are just scatter-brained, I would try reminding them again and expressing how much you'd appreciate their help.
If not, I would contact others, like you mentioned, but I wouldn't specifically mention the other professors unless they asked you outright why your letter writers aren't helping you. I would just phrase it like, "I'd appreciate another set of eyes on this," or "I'd value your insight," blah blah blah. That would probably make them more likely to want to help than seeming like you're tattling on the other professors (although obviously you have every right to be irritated at their lack of help).
Just my opinion, but hope it helps!