We're a family of 5 as well (me, DW, DS (13) & twin DD (11)). The category 4 verandahs fit us & the category 8B ocean view (large porthole) as well. We have no problem doing the 8Bs for a short cruise, but for longer ones we prefer the verandah to have just a bit more elbow room. The configuration is great for both the cat 4 & 8, pseudo bunk bed with a murphy bed for the kids while mom & dad get a king sized bed. Honestly, there's not much difference in price (big picture) between the two categories.
If you want to splurge, you can go Concierge, but that's a
very large price difference (thousands of dollars).
You could also go with 2 adjoining interior rooms and for administrative purposes have dad in one room & mom in the other while splitting up the kids accordingly. There's paperwork there to insure you can take the kids off (very weird, but understandable rule; more on the
DCL site). The cost difference seems to be more expensive than a cat4 (at least the times I've explored for our fam of 5).
The a, b, c... for the category tells you where in the ship you'll be (fwd/midship/aft).
We took a short 4 night to see if we liked it...beware. It's amazingly addicting.