Could you propagate a customised family apple tree?

Thanks for the interesting enquiry. The answer is technically "yes", we could create a bespoke family fruit trees ... but it would take 2-3 years to reach the same size and the resulting tree would be very expensive.

If you want to fit several apple trees into a small space, a better alternative might be to choose varieties grafted on the M27 rootstock, which keeps the height down to around 6ft. This article might help: In praise of the M27 apple rootstock.