You have an unfortunate situation here, my sympathies. I am not an attorney, but do have 35+ years of self-funding experience. I have some thoughts for you.
You should collect all the plan documents, this is where some of your questions can be answered, and your attorney will ask for them too. It is quite possible that Anthem is acting as an administrator here and not the fiduciary or Plan administrator. Because this is a self-Funded plan the employer can design benefits as they want, so it may be possible that Anthem covers these expenses in their fully insured plans, but not for this group.
There is at least one other person on here who could be of help, on the legal aspect, and that is Chaz, hopefully you will get a reply.
Good luck.