K.B.
Be your daughter's MOTHER... If you have to "give up" that "being her friend" part then do it. I am not sure why or how you can be sharing each others clothes. She is a CHILD she should have child clothes, you are an ADULT you should have adult clothes.
Be her parent, my daughter is only 4 years old and at times we are "friendly" like friends BUT she know I am always her parent. I want her to have an open communication about anything with me but if she is saying or doing something that I do not agree with as her mother I say so! Sound like you need to be mom and mom only since your daughter is having a hard time with her moods, she is having a hard time understanding why you are switching from friend to mom mode... you HAVE to be mom first so she has a stable person in her life.
On the topic of your son... THERE IS TONS of information about night terror, they are not going to give you a clearn answer on how it can be "fixed" because there is no one answer for everyone. I have night terrors, and I still do but as a child it happened often, now it only happens once or twice a year and it seems to be the same similar situation. Here is a great website to look at that will help you start working out what might be the issue http://www.healthscout.com/ency/68/341/main.html
http://sleep.lovetoknow.com/Night_Terrors_in_Adults
http://www.suite101.com/content/dealing-with-adult-night-...
I strongly suggest that at least your son talks with a doctor about the night terrors, usually by his age they have stopped or are VERY minimal. If you have gone to a few, go to different ones, maybe do a sleep study. Maybe everyone needs to see family counsling because everyone seems to be immature for their ages, I am sorry if that is blunt but it may be the thing that really helps your family. Also having friends the same age instead of mom as a friend might be healthy for your relationships.