The only people you have to tip are:
Dining Room Server $4 per day/per person
Assistant Server $3 per day/per person
Head Server $1 per day/per person
Stateroom Host/Hostess $4 per day/per person
When you order roomservice you can tip the person that brings the food, the way people tip this service is very different. Some tip $1 per person and some $1 per delivery.
Some people tip also the kids club people but then it's better to give a present instead of an amount of money. When the people from the kids club are tipped they need to split it with the rest of the counselers, to avoid this tip a present (giftcard) with the name written on the card.
Hope this helps.