This must be terribly hard for the rest of the family. Your mother seems to have lost sight of the fact that you all suffered the same losses. Instead of joining with you in healing grief, she seems to have retreated into her own. In that sense, you’ve lost your mother too. I’m so sorry.
If you possibly can, the family needs to band together to support your mother in getting treatment. Although her behaviors are consistent with a diagnosis of depression, the source of that depression may be more than the grief reaction alone. There are a number of physical problems that could be contributing to her problems. I recommend that you start with a complete physical checkup. She’s at the age when hormones can be out of balance. If she hasn’t been eating right, she may have nutritional issues as well.
If everything checks out medically, she needs to see a psychiatrist and a therapist. If she won’t go, make an appointment for the family. You all need information about how best to help her and you deserve some support while you try to make some changes. Tell your mom as lovingly as you know how that you are all terribly worried about her and that you are seeing a therapist to help you know what to do. Invite her to join you in helping the family recover from the losses and moving on. Remind her that no one is blaming her; that you all most certainly do want her back in the family.
As we get older, the generational roles begin to flip. As you were growing up, your mother did many things to keep you safe and help you grow, including some things you didn’t like. Now that you “kids” are adults, you may need to take the lead and take care of her. I hope you will be there for each other.
I wish you well.