Hard to say without knowing how fast those OGs veg and how much they stretch during transition. Ideally I would go for 18 plants, as in 2 x 9 plants. 3x3 plants on 4x4. Top all plants down to 4 main colas. 36 colas per 4x4. You could veg them in the 2x2 for the first 4-6 nodes, them remove the top so there are 4 branches left, then put in larger space and veg there for a week or so. 2x2 is obviously a small veg space for 4x8 flower, works best with more sativa/haze dom varieties that do most of their vegging on 12/12 during transition. Depends on the grow style too, hydro, especially something like nft, vegs faster and depending on strain and clone size sometimes needs no veg time at all.
The high end of that estimate is very doable if you utilize the space well, which is the case when you go for 36 colas per light and spread those out somewhat uniformly. Obviously 6 plants per 4x4 can work just as well, just use larger pots and top down to 6 colas per plant instead of one, and veg a little longer.