Just don't go too crazy... No need to cause lag from all the mobs/fires. Also, considering Blaze's first two attacks tend to go to the left and right, they'll cause a bigger fire than you might expect... Finally, I probably would have picked Ghasts, since they start fires and would blow a hole in the wall, meaning you'll have to build to get farther instead of just hiding and waiting for the vines to regrow. Although, Ghasts are easier to deal with... in a way...
kind of both, he had converted them to anvil but my Minecraft had to convert them so that i could play them, also infernal sky spawns you in a forest about 50 blocks from the victory monument (off of the islands).
If Minecraft (the latest version) is converting them then they definitely were not already converted to anvil.
Are you playing vanilla Minecraft? (no mods)
What maps specifically are you having problems with? (version number too)