I'm a parent of a toddler, so I feel the pain of parents flying with their kid. But WTF with changing diapers in your seat? Even if your family has the whole row, you are a jagoff. Let's take that business to the bathroom.
As for a couple getting an aisle and a window, my wife and I would always book that way with the hope of having an empty middle or that the person booked there would relocate. If it was full, we always would switch with the middle person. I can't believe people wouldn't switch. Those people are jerks.
Booking that way is still a #### move.
You're taking the aisle and window seats, which fill first. Now single travelers are forced to pick a middle seat. If they happen to hit your row, then you claim you'll move. So now the single traveller is forced to ask you to move to the middle, which you should have done in the first place.
Book two seats next to each other. If there's an open aisle, then you can continue your bitter marriage by having a space between you.
Couples are the only people on the plane who should be comfortable sharing their personal space. You're being selfish d-bags by booking this way.