My best attempt at answers:
Yes they add the 18% gratuity to each bill. (I don't think they would count your 6 month old, so you probably won't get the automatic 18%)
You do get 2 receipts at the end: 1 with the zero balance and also tells you the amount of TS meals you have left. (The CS balance only appears when you get a CS receipt). The other receipt is for the 18% gratuity, which you can pay by cash, credit card, or charge to your room, if staying on property.
I hope I answered what you needed to know!