Trivial additions are generally not shared, but 4 directions of 4 animations + 4 direciton death sprite + UI icons are hardly trivial. Yes you should share those. People would love them. 

I recommend using the same license as the original MiniWorld Sprites, (CC0) for compatibility. however CC0 allows you to use any license you want. It's up to you.

Recommended steps for sharing:

1. organize the additions you've made. gather the sprite sheets and icons that you modified. e.g. /Common/Tiles.png, but remove all the sprites you did not modify or add.
2. Upload them to https://opengameart.org/node/add/art
3. Indicate in the description that they are based on Shade's MiniWorld Sprites, and include a link to the original submission (just as you have done above)
4. Indicate in the description that you have used these in your game "Return From the Tavern", and inlcude a link (everyone loves to see assets in use, and you get to advertise your project)
5. Add the following text to the "Attribution/Copyright Notice" section:
   Based on "MiniWorld Sprites" by Shade, CC0: https://opengameart.org/content/miniworld-sprites additional animations & UI icons by Irog
6. Add a comment to Shade's submission, like "Hey, I added some new animations to this. Check it out [link to your new submission]" (this lets all the fans of MiniWorld Sprites know there is new compatible content available)
7. If you happen to create additional additional sprites later, edit the submission and include the new content as you create them. :)

for the link to your itch.io page, change the Attribution/Copyright Notice to:

Based on "MiniWorld Sprites" by Shade, CC0: https://opengameart.org/content/miniworld-sprites additional animations & UI icons by Irog: https://irog.itch.io/

I recommend also adding a blurb in the submission description that links to your itch page as well.

CC0, and OGA-BY permit DRM, so I recommend CC-BY 4.0 which forbids DRM. CC-BY-SA also forbids DRM, but it also requires share-alike, so it has slightly lower adoption rate (how many people use your assets)