What a complicated situation. You are in the middle of a family where people escalate arguments very easily and hold grudges.
I can offer you a few suggestions:
Remember that it takes 2 to have an argument. There is no point in staying on the phone for a 30 minutes argument. When speaking with your daughter, emphasize the positive. If she picks a fight, simply say that you aren’t interested in fighting and that you love her very much. Then say a friendly goodbye while letting her know you will be happy to talk to her again.
Don’t get caught up in drama: Stay out of your daughter’s relationship with her mother-in-law. Gently tell your daughter that your relationship with your husband’s children is not something you can discuss with her. Stay out of your daughter’s problems with her husband except to validate her concerns about her marriage and to applaud her choice to get into therapy.
Your present husband has a role in the problems. He rejected your daughter’s attempt to acknowledge him when he refused to take part in her wedding. He lost his temper and hit her. His apology is a good start but only a start. I think you and your husband need more help than I can offer in a short response. A therapist will provide you and your husband with on-going support and practical help as you navigate so many complicated relationships. You’ve tried your best to manage all this on your own without success. You both deserve the ongoing support a therapist can provide.
I wish you well.