Try unlinking the twitch account from the ESO account page, then immediately relinking. It seems to be triggering the email and the rewards for some. After you see the email, be sure to log out and back into the game if the rewards do not show up right away.
Yeah, it seems to require unlinking and relinking. I remember someone posted an image of a message from ESO (perhaps from Twitter?) where it said some people might be getting emails this past Friday about having to (IIRC) unlink and relink their ESO and Twitch accounts due to a glitch that had affected some ESO/Twitch accounts. I don't think I got that email, but it's probably a good idea for all ESO/Twitch members to unlink and relink their accounts just to be safe.
I read in the other thread you can't use an Amazon family account or something like that. Only one redemption per household.
Don't know the details as I don't know what an Amazon family account is.
I have Amazon Prime on an business account with my personal account attached to that. It didn't work for me when I tried using the personal account and I decided I didn't want to link to the business account. With the family account you have family members share the benefits on their accounts. Probably only account eligible though is the original account that was used to join Amazon Prime. Just a guess.