Failing classes in school is a scary thing at their age because it indicates that they may not have a clear understanding of what society expects of successful people. Most medium level jobs these days require a college degree just to land at lower middle class wages and eventually own a home. Their mother probably is doing the care-taker thing because it is all she knows how to do. A unified front before these kids will go farther than anything you can do on your own. And I dare say that their very futures are at stake.
ADD can be a wonderful tool for a person who enters adulthood knowing how to use it.
It is a big detriment to those who do not understand what it means or how it makes them function. Those who can use their ADD and do not mention it seem to go far. Those who are always asking for accommodation get accommodated, but I have seen few of them trusted with higher levels of responsibility and the pay that goes with it. It is not politically correct or anything else, but it is the way the real world works at this point in time and we need to prepare our children for it. Your real goal, based on your question, is to get them to understand that you love them and want what is best for them.