My Mom (85) health is declining but she refuses to give a power of attorney or medical directive to any of the 8 siblings?

As long as she can make her own decisions, that's what's going to happen. When she can't, possibly your state has a "line of succession" for healthcare powers of attorney. According to PamStegman, forty states have that. (Thanks, Pam.) Google Adult Healthcare Consent Act (your state) and see if you find something. According to this link, that's what it's often called:

Yes, been there, done that with mother in law. Are you all on the same page ( can't possibly be with 8 kids, can it?) Mom may be trying to keep peace by not picking one over the others. If you can all come together and present mom with a plan that you've all agreed upon, she may agree. Otherwise, if she's of sound mind, please point out that the state may step in and appoint a conservator.