8 dives over 4 days is fine, split 3 days North and 1 day South. After all, whether North or South, if you disregard divesites inside the lagoon, there are basically just three dive sites: the pass, and the sloping wall dives on the outside the atoll at each side of the mouth of the pass, altho there are many variations on which path the dive guide takes to get into the pass.
And even tho the passes are dived ideally with the incoming tide, at least in the South I have done it several times with the outgoing: you will still see a lot of sharks but they are more scattered and the viz will be less because it is lagoon water flowing back out to the ocean. Diving it with the outgoing is usually done by people staying in the South. If you are staying in the North and spending extra money and sitting thru the hour-plus ride from North to South, you want to dive it with the incoming tide. The dive operator you choose should know to when the incoming tide is. The other issue is that the dive operators in the North usually require a minimum number of divers (I think it is 4) in order to do the trip to the south.
In terms of quality of the dives, there is no question in my mind that if it is sharks you wish to see, the southern pass has the greatest wow factor because of what Sputnikboy said - it is a narrower pass and the sharks pack together more densely while facing the incoming current with the fresh, and clean ocean water. When I was last there in 2017, there was a team of French divers documenting the annual Marble Grouper spawn. They stationed cameras approximately equally-spaced all along the pass and triggered them to take one simultaneous snapshot of the section of the pass in front of them. When they tallied up the number of sharks at that one moment, it was well over 700 sharks inside the pass. By my eyeball estimates, the most I have seen in one pack while sitting in one place is maybe about 200 within my field of view. The other thing that is also impressive is the amount of fish life all along the sloping wall and around the piers of the Tetamanu Resort as you start ascending and doing your safety stop.
The above is not meant to downplay diving the North. Because of some really bad luck with three back-to-back storms in 2015, I spent 8 straight days diving the North and was never bored. I have seen equally impressive schools of densely packed sharks while diving the Northern pass too, but I attribute that to a very good dive guide and a lot of luck - I don't think that it is an occurrence seen everyday . Perhaps because I have had more dives in the Northern pass than in the South, I have also seen mantas and Great Hammers in the North that I have yet to see in the South.
Also as mentioned by Sputnikboy, the Northern Pass also has an area inside the pass that some call Alibaba and a few call the Valley. I have always dived this as part of the pass dive, not as a separate dive. I prefer "the Valley" because it is somewhat descriptive of what the area looks like. You are riding the current above the reef: sighting and approaching from a distance what turns out to be huge clouds of fish is the first hint of what lies ahead. Once you drift to the edge of the coral, you dive down maybe 10 feet into a sandy clearing below. You slowly meander your way thru the area while hugging the bottom to lessen the push from the current, on occasions hiding behind a coral head, all the time admiring all the fishlife around you and the handful of sharks hovering above. It is a very unique place: there is nothing that I can think of that is comparable to it elsewhere.
You asked about the corals: I don't think that you will be disappointed seeing the corals on the outside dives whether North or South.
One last thing to consider: Staying North gives you more options as far as accommodations, eating places, stores, and non-diving activities (not that there is a lot) to do for you, and especially for your husband and kid. At many of the lodgings, they have bikes for free for you to ride into the village just to poke around. Conversely, accommodations at the Tetamanu Resort in the South are rather rustic with no AC and no hot water, and there is nothing else there besides the resort, the water and the remnants of what used to be a small village.
I have never been there during humpback whale season so I don't know about the chances of seeing them. But September is their winter season, and the humpbacks do visit the area, so........