How'd they find enough parts to make a catapult?:

The catapult was made by a button, a wooden toy block, a rc car (That was broken off by extreme, the flavor blasted one in the first season) a paperclip, a piece of string, and a few other toy pieces laying around. You see, the under the bed area is very messy.

Why are they alive?:

Maybe it will be revealed later

How haven't they gotten stale yet?:

Maybe they are stale but nobody knows cause they haven't gotten eaten yet

How'd they build a stage that size under the bed?:

The stage was part of a toy. All they had to do was set up a sign and a few other things.

How can they build things at all?:

With their mouths