Lots of different answers to that question.
It depends on what is most impostant to you.
You could book a suite (cat 1 or 2)
All of you would be in one room
Expensive option
Or you could book 2 rooms:
Connecting rooms are available in Cat 4-10
10 is the least expensive option, inside cabins, no porthole
9 would be a little more money, but would get you some natural light
8 same as 9 on a different deck
7 is the least expensive option if you want a verandah (navigators verandah)
6 if you want the full open balcony
5 same as 6 different deck
4 a tad more space but for a lot more money
If your kids are older and you're OK with them being across the hall from you rather than in a connecting cabin it opens up more possibilities:
Cat 9 w/cat 10 across the hall (deck 1 or 2)
Cat 8 w/cat 10 across the hall (deck 7)
Cat 8 w/cat 11 across the hall (deck 5 or, 6)
Cat 6 or 7 w/ cat 11 across the hall (decks 5, 6, 7)
The least expensive option would be 2 Cat 11 rooms, but there are no connecting cabins available in this category
I didn't include cat 12 cabins since you cannot pick the location of those, so it's possible that your cabins would be nowhere near each other.
Edited to add:
If you do go with different category cabins book 2 people in the most expensive cabin and the other 4 in the least expensive cabin.