The first bit of advice I can give you is to post on Parent Emeritus, the forum for parents of adult children. Welcome to our rather close and helpful family. We have been there, wherever you are. The board you posted on is for parents of minor children which, of course, is different.
The next thing I have to say is NO MORE OF HER LOSESR BOYFRIENDS LIVING WITH YOU AGAIN EVER!!! NOT FOR ANY REASON! She is disrespecting you by this and you are allowing her to treat you like garbage. Don't EVER allow that again. You are a good, caring, too softhearted person who does NOT and SHOULD NOT ALLOW your adult daughter to yell, swear, scream at you and...dare I suggest...maybe even threaten to assault you or steal from you. This is YOUR house, YOUR castle and she is privileged to be allowed to live there. You can revoke that at any time. She has no business bringing criminals into your home where her own daughter also lives and you really should not ever allow it. It's a threat to you and your granddaughter and your daughter is too selfish and me-centric to care. She is what she is. You have to take care of yourself and your granddaughter, not her.
There is NOTHING you can do to change your daughter. She has to change herself of her own accord. The best thing you can do is to stop rescuing her when she falls and to let her write her own life's story because you have 0% control over anyone except yourself. You have 100% control over how you react to her, but you can't change her. I have no idea why you want to meet her loser boyfriends. You can't stop her from dating them. You CAN decide to stop letting her live with you and take other action to protect your granddaughter, but you will not change your daughter. She could be using drugs by your desceiption of you and, no, she does not really care about being a mother. Why should she? YOU take care of her daughter. She doesn't even have to worry about her daughter and I'm sure she gives her child little thought when she is with her newest Mr. Wonderful.
She sounds as if she may have borderline personality disorder. Has she ever had a diagnosis of any kind? Borderlines can not bear to be alone and are able to quickly turn people off and on like a TV channel so when she has a boyfriend, he is her world and nobody else matters. She would also be highly dramatic, very immature, and and me-centric. It does not sound like her daughter comes first.
Now if you want to continue to allow her to live in your house, many of us have told our adult kids "My house/my rules or pack your bags." You can insist that in your house she has to be home by 10pm or whatever time you want. You can insist that if she leaves the house you will lock her out and sh e will have maybe two months to find a place to stay or, whether she has a place or not, she is out. At the same time you can call CPS to report that she is not caring for her daughter and, if you want to, perhaps you can end up with custody. If you don't want that, there is foster care. Or your daughter can sign over guardianship of the granddaughter to you.
Worrying about her won't change her one wit. Are you in therapy for yourself to learn how to cope with having a difficult grown child? Most of us need it and get it!
There are big questions you have to ask yourself such as how many years to want to be a mommy to your adult daughter? Many of us have decided we want a life, even though we had struggling adult children. Many of us have decided we won't parent anymore and we will allow our young men and women to be adults and figure it out themselves, even if they stumble. Other people take care of their c hildren forever, even when they are eighty-five and their adult "child" is sixty years old and still unable to take care of himself. To me, that is a very sad scenario. Usually these adult children do not care about us except as the ATM and White Knight rescuer.
But it IS an option.
Our adult children are great at turning everything around as our fault. Their crummy life is our fault. Don't buy it. It's a load of trash. Don't engage your daughter if she tries to argue with you. Walk away or leave the house or say, "Sorry, I'm taking a shower now" then do it.
As for your daughter's many boyfriends, a symptom of borderline which she may have or may not have, that isn't your business who she chooses to date. If s he picks losers, she picks losers. I would not waste one word about her choice of losers to her. She is not going to listen. She is not a little girl and when it comes to making her own bad decisions, she will not listen to you. So I would just say, "I am not going to listen to you talk about Loser from now on. But he is not allowed in my house. Remember, this is MY house." Yes, she will be mad. She may had a two year old meltdown. Too bad. Call the cops if she gets violent.
Anyhow, I hope we can learn more about your situation and I do recommend you post on PE rather than here.
Hugs for your poor, tired hurting heart. Have been there, but come out feeling great with a very blessed life and you can too.