His most recent actions - blowing up at your DIL and contacting all her friends and family in an underhand manipulative smear campaign is in my view (and I hope your DDs) the final nails in his coffin.
This is how coercively controlling and emotionally abusive he is.
He is emotionally incontinent.
She needs to feel strong and proud and think how she would feel if she got a similar call from a friend or family member - most of us would look at this a shocking, disrespectful, covertly bullying behaviour - we would not be interested in listening or being involved in such inappropriate nonsense. We would feel very concerned for the other party.
She has no shame or guilt or obligation to weigh her down - she should be confident that she is a person or integrity who has been stolen from, lied to, deceived and abused.
This latest shameful behaviour is all his.
Detach and block.
He is worse much than you thought. She could tell her work place, gym, friends and family that if X gets in touch they should respectfully not engage.
Anyone will see he is vile, unhinged, desperate and abusive.
She should consider sending him a single cease and desist instruction where any further communication to her, her family, friends and workplace will be reported to the police and military as stalking and harassment.
He needs his wings clipped.
Expect this to escalate.
He’s a nasty a bully. Pace yourselves and protect your DD.
He is out to punish her for this.
Know that. Get him on notice.
Sunlight is the best disinfectant.
100% NC is the only way forward. Any info or inch he will exploit and take a mile - as he did with your DIL.
See your sadness as grief for the person you thought he was and the future they should have had together if that’s who he was.
He wasn’t who he said he was.
He never was.
He never will be.
This is who he is - an abusive, emotionally violent, gaslighting, thieving, rage-full, lying, manipulative, nasty fucker as proven by his consistent repeated actions (ignore his words).
The addiction is probably the least of her worries. Some addicts are “nice” - as in calm etc - this bastard is first and foremost a thug.