I’m so sorry that you (& your twin) are having all these issues & are in so much pain, you certainly have a rough deal 
I don’t know if you’ve tried sleeping more propped up, it often does help with neck pain, but I don’t know if you can do that with your back? There’s a current discussion about the best wedge pillow:
Best wedge pillow on amazon - General - Living with Eagle
Some members have tried the soft collars to keep their head in a better position, so whether that’s worth trying?
Can you take muscle relaxants, or have you tried them before, it might help a bit?
@vdm has posted alot about exercises to help with tense muscles & posture, that might be helpful, here’s a link:
List of my favourite resources on YouTube to learn anatomy - General - Living with Eagle
Sending you a hug and hope that you can find some relief
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