Did you thin the trees? On average you would want a fruit every 6 inches. Doubles are ok but triples tend to hurt size. In general apples will have 5 flowers from each fruit bud(center flower is called the king bud which is surrounded by 4 secondary flowers), if you have good pollination and every flower develops into fruit sizing will be poor. Commercial growers have ways to deal with that with growth regulators and lots of praying for good weather
With your 3 trees you could hand thin. To do so wait till king bud fruit is about 1", they should be the biggest fruit, then take off whatever fruit you need to so that it averages out to 6".
The grafting I have done, we harvested the graft wood in January, dead of winter. Kept that wood refrigerated until spring. After trees leafed out we grafted the dormant shoots to the tree. We always used grafting wax to seal so not sure how epoxy would work. I know there are other methods that I have not done but I could not cut graft wood this late in the season for how we did it. That said, give it a shot on a limb or 2 if you have nothing to lose. Keeping the graft wood from drying out before they connect will be the biggest problem.
Honey crisp is a great tasting apple, Dont blame you for wanting to try that. Just a heads up, they are more difficult to grow for #1 quality fruit. That has been my experience. Hope that helps you out some. Good luck if you go to graft. Wish you success! Keep us up on how it progresses.
Mike
