A: I think you should. Most toddlers I know leave a large trail of debris in their wake (raisins, spilled milk, crayon wrappers, etc.). Your cabin steward and waiters will probably spend more time picking up after your son than all the adults in your party combined… and in my opinion, that merits a tip.
Q: My parents are retired and on a fixed income, but my dad still makes a big deal about paying for the whole family when we eat out together. If I ask for the check he'll grab it out of my hands. When you're dining with a multi-generational family group, who should pick up the check?
A: In my experience, that honor belongs to whoever can grab it first (and then win the ensuing "No, let me get it!" argument). I'm sorry, but there's no hard-and-fast rule like "the oldest person who's currently employed should pay" or something. What I will say, however, is that if you really want to pay without someone trying to overrule you, it is possible—as long as you don't mind a bit of a covert operation. Get up as if you're going to the bathroom, find the maitre d', explain that you want to pay for your table, and give him your credit card. At the end of your meal, your waiter will bring the check to you—and it'll already have been run on your credit card. Then it's pretty much impossible for your dad to claim it.
Q: What do you do if you're staying at someone's house and the guest room isn't comfortable—like if the bed has an ancient mattress and it bothers your back, or it happens to be the one room in the house without A/C or something? Is there a graceful way to move to a hotel?
A: Now that's tricky. In general, when you accept someone's invitation to stay in their home, you have to deal with the accommodations you get. That might be an air mattress, or a futon you remember being in their college dorm room, or a room with street noise. Tough luck—if you want a hotel-quality room, you should stay in a hotel. When you don't like someone's guest room, I think your only options are to suffer through it or make up some excuse why you have to cut your stay short and leave town. "On second thought, I'd rather stay at the Ritz" will probably hurt your host's feelings (especially if the main reason they invited you was to spend time with you).
The only exception I can think of would be for some sort of medical condition—you can't handle stairs, and the guest room's on the third floor, or you have an unexpected allergic reaction to your host's cat, etc. Then you can explain why you need to move to a hotel without making your host feel they've done something wrong. However, if your host does something to attempt to accommodate you—like setting up a sofabed in their living room so you can avoid the stairs—you need to take them up on it. And of course, it's much better to take these things into consideration before you accept an invitation to stay with someone. If you know you're terribly allergic to cats, and your friend has one, it'd be much better for everyone if you simply plan on staying in a hotel.