Janet is 17. Contact her parents and explain that she came to your home while you were out of town and stole hundreds of dollars worth of food. Screencap all of her social media posts regarding your husband, particularly those threatening to contact his place of employment. Provide Janet's parents with them and explain that if an immediate end is not put to this, you'll have to contact a lawyer as she is libeling your family and threatening their well being- and most importantly, follow through and get those screencaps to a lawyer if her parents aren't responsive.

I'd suggest teaming up with your husband and banning Janet from the house altogether. She stole from you and was completely unrepentant about it.

As for Hailey, you guys definitely need to talk. Your husband may be taking the lead, but her attitude and behaviors have a huge impact on your younger children. You said she quit soccer recently- it might be helpful to fill that void with a different physical activity like bike riding or running. Make an effort to expose her to healthier lifestyles. Cook healthy meals. She could be at a tipping point in not only her weight, but her approach to it. It sounds pretty strongly to me that she's given up and may be feeling sad or frustrated. She needs your help and support now before she settles into some really bad habits.