Flamenco is a late season apple, for December to February, but it needs a pollinator. I guess as you have apples then something is successfully pollinating it nearby.
Although you won't be harvesting them for some time, golf ball size by August is very small and I doubt they will grow to huge size by the end of the season.
Growing anything in a pot can be tricky, fruiting trees particularly so. Is the 14 inch pot a deep one or shallow? I'd certainly put it in a larger container in the autumn before next year.
Apples grown in professional orchards here are drip irrigated and fed throughout the season; that's how they get such large heavy crops on relatively small trees. If you adopt the same approach with a drip irrigation, ideally with some liquid fertiliser mixed into the water, then you will do better next year.
Also used a soil based compost rather than a peat or soilless one, something like John Innes No.3.

I have checked the pot I am usiong for my Flamenco apple tree and it is 22" diameter and 18" high. Do you think they will grow to a reasonable to pick in December?

All I can compare your Flamenco apple to is a late season apple we grow called Delbard Tardive. (late Delbard). The apples on this which are harvested in October or November are already almost full size so I would be surprised if your Flamenco ones will grow too much more. Perhaps this is because you have too numerous a crop on a tree which is too small, and apple thinning might help next year too. The pot sounds large enough to grow a perfectly healthy tree with feeding.