What a complicated situation. Your husband is asking a lot of you. Not only are you taking in these difficult young women, but he is apparently not giving you any help. He needs to let them know they have to be civil to you. You are trying to engage these girls in life, but they and their dad aren’t joining you in the project. You can’t be their therapist. You can’t be a surrogate mom. All you can be is a caring adult. But you can’t do much, if your husband isn’t supportive and the girls won’t accept your care.
The girls need treatment if they are to get better. I hope they are taking medication. I very much hope they are getting some therapy, especially the girl whose mother committed suicide. Mental illness may or may not run in the family. But your husband is giving his daughters a terrible role model for how to treat other people.
Most important, he needs to get involved with their care. If he can’t or won’t, you need to find a way to protect your own feelings when these young women are disrespectful. Do stay out of arguments with them. You can’t win. By all means, invite them to go places with you, but don’t take it personally, if they turn you down. And don’t plead with them. Invite them once, then go about your own business. Take a deep breath and step back emotionally.
As for your final question: If your husband lets you know that he thinks about hitting you, he is threatening you. That is verbal and emotional abuse. Regardless of whether the girls get off on their own, you may want to rethink this marriage.
I wish you well.