It is wrong for your mom or dad to ask you to take sides. I have done this myself with my own daughters and they have called me on it. When I have done it they would say something like the following:
1) Mom, I am your daughter and you should not put me in the middle of your fight with Dad. This is between just you and him and I should be left out of it.
2) It is wrong to tell your personal problems to your kid. You should not be telling me this.
These statements stopped me dead in my tracks. It made me think and then feel bad because they were right.
You can try saying something like my kids have and see if your mom and dad stop putting you in the middle.
You can recommend to your dad to purchase these two books for your mom . They have really helped a lot of people on this board. The first is by Anne Gittleman, called "Before the change, taking care of your perimenopause"
And "What your doctor may not tell you about premenopause" by Dr. John Lee. When it comes to premenopause doctors don't do much to help. These books tell you what you can do for yourself at home (vitamins, supplements, exercise, etc.) to help alleviate premenopause symptoms.
If your mom sees a doctor for her depression and gets medication and she tries the things suggested in the books for premenopause, then she should start feeling better.
I know what you are going through because my mom too suffered from severe depression. I hope she feels better soon.