Wow, theses are beautiful! And charming! The thumbnail looked like a digital painting. So great to see such creativity in non-digital pieces once in a while (even though I love digital, too. it's just become the norm and therefore kinda dull)
So, The one on the left reminds me of Spongebob - Squidward's house, the one on the right reminds me of DragonBall Z - King Kai's planet, and the middle is like a combination of Kame House and the island near Bikiini Bottom.