Hi Shy
You have already done most of what I would have recommended: seek professional help, avoid stressing the elbow and wrist areas and try some anti-inflammatory agents. I am not a doctor and don't know you so I am not sure there is much I can add to help you, but let me venture a few suggestions that you can check out with your health care team.
First for anti-inflammatories: you could try some Ayurvedic remedies, such as making a "tea" with turmeric (~ 1/2 teaspoon per 1/2 cup of hot water). Try it twice a day for 5 days or so and see if you notice an improvement. You could also trying Earthing (check out this
web site for why and how). I can personally vouch that both of these treatments have worked for me.
Secondly for modifications: for cubital tunnel syndrome, you would have been advised to not place any pressure on the inner elbows, so doing Down Dog on your forearms may not be great! However, because of your carpal tunnel problem, doing regular Down Dog would not be great either. Have you tried doing all these kinds of poses where you are putting pressure on your wrists and forearm while holding your hands in fists? The idea is to keep one straight line from your forearms to your big knuckles; no bends in the wrist at all. This means that you would be putting the weight onto your first two knuckles, not the last two. Try it in Cat first to get the feel for it: remember - no bends at all at the wrists in any direction. Have the palms facing in towards each other so that the knuckles are facing the sides of your mat, not the front of the mat.
Neutralizing the angle of the wrist should help with your carpal tunnel problem and not bending and stressing your elbow joint may help with your cubital tunnel problem.
I don't know of any Yin yoga poses that will specifically help these problems, but all yoga does help with overall health, which has to be good for you in general. You could review my articles on
Yin Yoga for the Upper Body and see if any of these help. My best suggestion however is - find a good Yoga Therapy teacher and work with her in person.
Good luck!
Bernie