The situation you describe is not only frustrating but heartbreaking. You and your fiance are trying to build a family and you would like your mother in law to be a part of that, but it sounds like she is making it difficult.
I think it would be a good idea to sit down and talk, the three of you. I would recommend that you let your mother in law know that the purpose of your meeting is to discuss building positive relationships.
You should list the behaviors that have been upsetting, but try not to include every little thing. Stick to the themes or patterns of behavior. When you talk try to be matter of fact, not accusatory. Try to keep emotions to a minimum. Stick to the facts. Set up rules or guidelines to your discussion at the start.
I would love to have a positive relationship with her but I at this point I don't know how that is possible. She is one of those people who is dripping with sweetness but talks about you like a dog to others. She has screamed at me and my children, disrespected us, said hurtful things, said she will not stand by and see him marry me.
at this point I do not like her at all. but I love my fiance. Should I be the one talking or should he take control and list those things and set the boundaries
I have tried several times....listened to her apologizes and watched her do it again.
It may be a good idea for you to do it together. Be a united front. Your goal should be a civil relationship at this point, if it becomes more positive that would be a bonus! You and your fiance need to draw the line in terms of what is acceptable and what isn't. Having a meeting where you discuss this would start drawing that line.
You and your fiance need to give the message that if she is hurtful to any of you that you will stop interacting with her. Hang up the phone, leave the room . . Let her know that you want to interact but you will not tolerate being hurt.
If this seems an overwhelming task, I recommend that you and your fiance seek family counseling to deal with this. At some point you could ask your mother in law to come to a counseling session. Sometimes having a third neutral person is helpful in these situations.
Good luck to you. Let me know if you have further questions.