It’s not at all unusual for long-married couples to re-evaluate their marriage once the children are grown. It may be that your wife has been unhappy for some time but hasn’t had the time or energy to deal with it in the midst of raising kids. Now that they all seem settled, she may be turning to her own desires and feelings. She may not be doing it in an appropriate way but it’s not an inappropriate thing to do.
This is between the two of you, not something to sort out with adult kids. They need to be kept out of the middle by both of you. She shouldn’t be talking to them about her unhappiness with you. She should be talking to you. You shouldn’t be enlisting the kids to gang up on her through a surprise intervention. You should be reaching to her.
I suggest you, alone, have a quiet talk about how sad you are about how the two of your have grown apart. Ask her with all your heart if she would be willing to see a couples therapist with you to see if you can reconstruct your marriage. Tell her that you are willing to hear what she has to say and to take your part of the responsibility for what has happened.
With some 30 years of marriage, it’s at least worth a try to see if you can put things back together.
I wish you well.