Wouldn't want to see these guys in a film... but it could work if a LOT of changes where made.
Though I would MUCH rather see them in an anime or another game, here's how I would handle each character. Well... I wouldn't say "character" as much as CONCEPT
1. Krystalak would receive a reworked look and a new name. I would rename the kaiju GORATH after the Showa film, similar to how Megaguirus was a rehash of the Meganulons. Design wise, he would look like this:http://rendragonclaw.deviantart.com/art ... -188263816
He would attack with a Cosmic Dust Shower attack from his mouth and exploding quills on his tail, for the most part fighting like the original Krystalak. Origin wise, Gorath would be a creature riding on a comet passing the Earth. Scientists attempt to collect mineral samples from the comet with a traction beam (or something...) and end up dragging the kaiju to Earth instead.
2 Obsidius is now a flesh and blood creature. Still working on the design, but he would be renamed Pyrodorah. He originates from the Earth's lithosphere, being brought up to the surface by a geothermal power plant a top a volcano exploding.