john,
You are doing the right thing, you aren't keeping this to yourself but bringing your situation to a body of believers so we can lift you up and pray for your family...which I will do. I will give you my advice and feel free to do what you want with it.
Your daughter needs professional help if she hasn't already. Contact a doctor, a helpline, and/or a trusted pastor for council. A godly woman who could talk to her also does worlds. People who are hurt try to hurt those around them when they feel helpless. Continue to love her and pray for her. Let her know how much you love her. 6 years is a long time and you do have my sympathy. I pray that the Lord interceeds in her life miraculously and gives her peace that surpasses all understanding. If she still holds hurt towards you perhaps family therapy would be a great way to rebuild your relationship and get the root of the problems she's facing.
Its understandable your wife is under intense pressure. The best way to relieve pressure I have found is to pray together. Pray with your wife undistracted in a room for eachothers safety, physical, and mental well-being. Afterwards share hugs throughout the day.
Your pregnant daughter seems to think she knows what she wants, but you better believe children go back to their parents when the going gets tough. Assure her that you're here for her when she needs you and that you love her.
Prayer is our direct link to God. God will always without fail listen to you. When everything feels out of control I read the Psalms of David. Pray these verses out loud and claim them in your heart
When the righteous cry for help, the Lord hears, and rescues them from all their troubles. (Psalm 34:17)
I sought the Lord, and he answered me, and delivered me from all my fears. (Psalm 34:4)
Hear my cry, O God; listen to my prayer. From the ends of the earth I call to you, I call as my heart grows faint; lead me to the rock that is higher than I. For you have been my refuge, a strong tower against the foe. I long to dwell in your tent forever and take refuge in the shelter of your wings. (Psalm 61:1-4)
The Lord is near to all who call on him, to all who call on him in truth. He fulfills the desires of those who fear him; he hears their cry and saves them. (Psalm 145: 18-19)