While a number of us may argue the ethics of holding seats for later-boarding passengers

, in this case, what the OP is going to want to do is have the first-boarding family members take the window and aisle seats. Most passengers won't take middle seats unless forced by circumstances (aka no more aisle or window seats available).
Question, though. The OP only lists five boarding pass numbers: A54, A55, A56, B02, B03. Was this a mistake, or do you actually only have five boarding passes for six people?
Also, um... oh, yeah. If you have small children who might have a tendency to kick (or pull on, or otherwise 'attack') the seat in front of them, PLEASE have members of your party sit in front of the children, instead of behind or across the aisle.