How do you handle a a disrespectful adult child, have done and tried everything and nothing seems to work the older they get the worst again, it is so hurtful and embarrassing, I pray for them constantly.
Do your children claim to be believers?
There is a passage in Leviticus that says do not hate your neighbor in your heart, but rebuke your neighbor frankly, lest you share in his sin. Then, right after this is the verse that says to love your neighbor as you love yourself.
I think it is important for a parent to point out to their children, even adult children, when they aren't honoring their parents. My wife is from a people-group in Indonesia where they like to give a lot of advice. I was watching an Indonesian TV show on YouTube recently, and the host of a game show was from her people-group, and I saw how he'd advise contestants and get on their case a bit with that same tone of voice I'd heard among her people.
One thing I'd notice is the parents would exhort the kids to honor their parents. Older brothers and sisters would give advice to the younger brothers and sisters. "Don't talk to your parents like that." They'd even do that to the young adults, tell them what to say back to the parents, right there in front of everyone. Those sort of social interactions would work too well if attempted in an American family, but it's interesting to watch.
And it hadn't occurred to me how important it is for me as a parent to teach my little kids to honor me. If I am to raise them in the honor and fear of the Lord, I have to actively teach them to honor me and their mother. It seemed a bit strange for me to hear my mother-in-law tell her adult son he needed to honor his parents, but I think there is a place for that. But even with adult kids, that's something you may have to remind them of if you have the chance to interact with them. If they are claiming to be Christians, then you have some common ground on which to exhort them. In Indonesia, I think just about everyone in the dominant national culture there would see the need to honor parents as obvious, something that nearly all agree on. But in the US, it's something the movies and TV seem to teach against. But Christians should believe in it. And if you had a chance to talk to your daughter-in-law, and she claims to be a Christian, then pointing out that encouraging her husband to stumble into sin by not honoring his mother is a really bad thing.
You could also tell your son you don't want him to live long rather than die young. Honor your father and mother is the first commandment with promise.
Other than threatening to cut children out of the will and just leave whatever you have to a church or a charity, all that I can think of is that you can pray and you can talk with them or have other people talk to them. You could also talk to their pastors/elders if they go to church.
If you live close to your DIL, cutting off a relationship with you is shooting herself in the foot. I don't know why a parent of small children wouldn't want free babysitting. That's a perk of living near grandparents. I'm kind of stuck right now, temporarily at least, away from either set of my children's grandparents. I would like to be near mine or my wife's so I could see them more or my wife could see her parents more.