I am going to make my suggestions after a norse theme. All names here are taken directly from norse mythology.
World 1: Midgard. Midgard is the land of the humans. The most populated realm but not the most peacefull neither the most agressive.It holds a certain balance.
World 2: Yggdrasil. Yggdrasil is the tree which holds the nine realms. It is an ash tree which was created at the beggining of time. In his branches and at his roots are the diffrent worlds of the norse mythology.
World 3: Vigridor. Vigridor is a large plane where the last battle of Gods and Frost Giants will take place. The world will crumble under the fearsome blade of Surtur, the fire giant. But after the battle is finished life will continue, humans will thrive again and Thor's two sons will lead Asgard after his death with the help of Baldr, Odin's long lost son. (I suggested dis because of World 3's infamy of wars and my hopes for it's hopefully peacefull future.)
World 4: Folkvangr. Vanaheim is the land of the Vanir, the gods of nature and peace. Folkvangr is their land for humans who've lived peacefully throughout their lives. There is no cold, hunger, illness, war or pain there. (Again, I've suggested this because of world 4's lack of wars and peacefullness, Stay awesome W4 <3)
You deserve capital punishment.