This is very simple to do, you are just overthinking it.
To combine two different style of artists, just include their names.
Code:
/imagine prompt: medieval fishing village on the ocean, dragons in the sky, painted by Salvador Dali, painted by Anton Pieck --ar 16:9 --q 2 --v 5.2
To combine two different art styles, include the names of the styles.
Code:
/imagine prompt: medieval fishing village on the ocean, dragons in the sky, Flat Design, Glitch Art --ar 16:9 --q 2 --v 5.2
And the same thing with themes.
Code:
/imagine prompt: medieval fishing village on the ocean, dragons in the sky, Claymation, Stop-motion animation --ar 16:9 --q 2 --v 5.2
You can mix & match but the more you add, the more muddled your images will likely get.
Include the "no" tag to keep the things you don't want, out of the image.
Code:
--no clowns, dwarves