Hi Amanda,
Stamping on the walls is actually very easy. Might be a little more difficult with the butterflies, but if it's perfect it's not homemade right?
Some people use craft ink and some use Acrylic paints.
I myself used acrylic on my DS's wall and it worked out very slick. What I did was take the stamp and a sponge and daub on the paint to cover the area then stamp. My walls are slightly textured so they aren't perfectly filled in like they would be on paper, but they are just fine.
As far as doing the butterflies (2 step stamping) I would wait until the first part is dry then do the outline of the butterfly on another color.
There is another trick too that people have done. Put paint a paper towel in a selected color then use the paper towel as a 'stamp pad'.
You can check out my son's wall in my gallery...
Gallery at Splitcoaststampers
Good Luck...
You can also call demo support and they could tell you what colors that were used.