Sounds like a typical family to me.....everyone in it has been thoroughly trained by example and knows one thing very well........how to push each other's buttons.
I don't think you should place much value on advice from strangers who very likely can't see their own forest for the trees in the way, despite their apparent distance from the problem. I say "apparent", because most of us have had similar conflicts with family, and will probably be addressing your problem from a personal point of view that might incline some of us unduly toward one side or the other, thereby discrediting those opinions in a way unknown to you.
Free advice is worth approximately what it costs you, especially if you know nothing of the perspective and background of the person tendering said advice.
As an example, I submit that it is very likely that if you were to survey those who have so far offered negative opinions about your stated position (and unfortunately in some cases about you as a person) you would find that they have never been a parent, are much closer in age to your sons, and therefore would logically more easily identify with them, vis a vis the parent/child relationship.
This is most overtly demonstrated by those who claim, for example, that parents need to respect their children by treating them as equals. Any sucessful parent (one whose children have grown up to be responsible, generous adults) knows that this is utter bilgewater.
Just as teachers should not have the same relationship with their students that they do with co-workers, and just as military officers should not treat enlisted personnel as equals when it comes to carrying out their assigned missions.
In families, just as in the military, somebody is supposed to be in charge and be allowed to delegate authority to subordinates. What is often neglected by those in charge, is that they must always be mindful that only authority may be delegated, and never responsibility.
It might be best, instead of my making the same mistake as others and taking sides based on so little info, that my worthless advice be confined to generalities and methodologies designed to improve communication.
To that end, I would suggest first that you do not use the spoken word in your subsequent interactions with your sons, but instead insist that they only communicate with you by email, until such time as some of the misunderstanding and antagonism has had time to dissipate.
Time.
It gives one a chance to consider possibilities and explanations of behavior other than the ones that reflexively leap to mind in the heat of verbal exchange.
Writing, instead of speaking out of the conditioned reflex that so easily locates the other's "buttons", gives one time to consider the best way to proceed -- and also comes with the cautionary knowledge that one may be held accountable in the future for what one says, for the written word is not lost upon the wind -- and not therefore dependent upon anyone having the ability of total recall to ensure that accountability.
It is this accountability (greatly mitigated among strangers here on the web) that will often prevent the hurtful, callously thrown words that result in broken homes and relationships among those we truly cherish.
Perhaps a cooling off period is warranted, though, especially given the most recent events during such a highly charged occasion as Mother's Day. I wouldn't be expecting any holiday to be greeted normally, which will save you from disappointment, at least until all this crap about money is resolved between you.
And that is exactly what it is.....crap.
Unlike others here, I would not recommend suing the ex for back child support, even though it is certainly owed. The time for that has long since passed, and if done now, would appear only to be an attempt to garner some of the windfall, and your own declaration of refusal gives me hope that at least you are somewhat aware of the appearances which must be considered, regardless of the financial cost.
Be grateful, in the meantime, for the son you have still have, and take solace in the knowledge that the others are still willing to try to patch things up, despite all the miscommunications and hurtful words.
But the best free advice on family matters I have ever heard consistently given to others is perhaps found on talk radio.......by
Dr Laura Schlessinger.
I sincerely wish you luck, and would only caution you against taking anything you find here too seriously.......after all, I am also a divorced parent and grandparent, so who am I to give advice?
Carry on.