To keep with the Aurumoth theme, I am thinking Argentomb for the second pre-evolution. Argentum is the Latin word for silver, which plays off of the copper > silver > gold progression and its coloration. It's also going through metamorphosis through a cocoon, which is like a tomb. Finally, it contains the theme of resurrection. It spends time in the tomb (death) before it is resurrected into the pseudo-legendary that is Aurumoth.
For the little one, I'm debating using Cuprumbee, based off of the Latin word Cuprum, which is for bronze. The -bee ending is kind of an allusion to bees, which keeps with the insect theme. Moreso though, -bee, when spoken aloud, is the ending of baby, which also fits into the idea of resurrection. I'm going for birth, death, and resurrection, along with copper, silver, and gold. Lemme know what you think!