Hi Alvin! I'm happy you like Minifantasy assets :)
I'm not really sure if they will work well with GB palette. My guess is that you will probably need to do some colour editing to get them fully matching the palette limitations.
Do you know there are 2 free asset packs? Minifantasy Dungeon and Minifantasy Forgotten Plains. If you didn't do yet, you can download both and do some test.
If you have more questions or want to speak further about it you can reach me in Twitter @krishna_palacio.
I would love to see it working in a GB game! ^^