Welcome to the wonderful world of chinchillas & the Club.
Your babies are still very young, how exciting for you.
I have never really used pee pans as such, mine are the full of the cage floor so I have shavings on the whole floor of the cages.
I do have some houses on the floor, though most will sleep up on a ledge, or in a higher house.
The only time they sleep on the floor is when it's warm or there are kits with Mom and then they don't stay down there long.
Most will pee in a corner while some of mine will pee right around the water bottle, hay rack, or food dish.
The older should teach the younger as she seems to not have learned yet.
I have never used bedding as bedding, but do put a fleece blanket in a house on the floor for moms to give birth.
Everyone does things a little different,and all chins are different.
We'll hear loads from you I'm sure. there is so much to learn and if you find one that knows it all lets us know.
I learn somthing new everyday.