I might find a mural for the wall at the head of the bed that melds the two themes...even just a night sky with the milky way or something like this:

Then let each child decorate the wall next to their bed in the theme they prefer, either more murals or wallpaper that coordinates with the original mural.

Or for a more affordable option, do the big mural and paint their walls in colors that complement it and let them get wall stickers to add in their preferred theme. Kind of like creating their own wall paper.

https://www.wallums.com/wall-decals/animals-butterflies-dogs-cats-birds-wall-decals/

Keep moving in the direction you are in. Paint the walls a neutral then let the occupiers choose their bedding, what they hang on the wall nearest their bed... It's a room in constant transition. Don't go too deep on a theme. As kids grow they change!!

thanks 🙏

Yes, I’m in rental home so can’t make too many changes, but bedding and peel and stick removable murals is probably when I will start.

Love the idea of letting them add their personal touch, glow in the dark stars etc. to help personalize. Thanks you both!!