I don't hold out much hope for your first chick... if it isn't pecking at things yet... you need to cull, it is starving to death slowly.
Once you are sure the sibling is going to thrive ( still need to see the digestive system is working), I would grab another chick from the feed store as a buddy if that is an option for you.
The whole wait until the chicks is fluffy before moving them thing is assuming that your hatch was normal and your babies don't have egg stuff all over them. Those with egg stuff may never naturally fluff up because it can be like cement.
Can't wait to see the next pic!