IDK why you would be looking to tip the MD (now DRO) who is quite removed generally from your dinner service. I'd be more inclined to reward the two waiters. If a HW does something extra for you, then I would consider that. Even a DR Mgr is up the chain for tips. Example: On a ship last Fall, he made extra effort to get us setup for same table each night and moved us on request. He refused any money I wanted to give him. In this case, he got complimented for providing the TD experience that Princess promises but must be asked for.
As for cabin steward, how much do we suppose of the $16 is allocated to the hotel staff versus DR staff, etc? I don't have any guidance there other than what you are comfortable with and based on services provided. Did you ask for a lot of extra things? Is the cabin often messy for them to clean up? Not applicable to your situation I gather, but is it a cabin where the sofa bed or bunks are used, so there is extra work?