Good question, and the first time this has come up; they only have a few, and only on four of the large ship: I found 18 each on Diamond and Sapphire Princess and 10 each on Island and Coral Princess.
The other large ships (including Diamond and Sapphire) have what they call "Family Suites", which are actually two connecting mini-suites all the way forward on Dolphin Deck. The deckplans don't show them as two cabins but that is what the footnotes say. There are only two of these "Family Suites" on each ship.
Hope this helps.
p.s.--I just noticed Penny's post about being able to open the partitions between the balconies; good point; I didn't think of that.