why is size so imperative??? are you having them professionally installed???? .. if not ... go small ... ken

What a beautiful tree! I had to look it up since I'd never heard of it. It looks like it can be grown as a tall columnar shrub as you have it, or tree-like with a canopy. The link says it produces the bright red leaves with maturity. Can't wait to see how it does for you in the years to come. Be sure and keep us posted.

If you do a web search for the topic of planting near pools a recurring theme will be the need to choose kinds like bananas and palms that don't produce lots of little bits of stuff that clog filter intakes. Of course, if you get another killer winter anytime soon subtropical types like these will fail. And it's not unusual for eye opening winters to come in clusters. So what you probably need is something filtered for big parts + cold hardy. What grows natively around where you are, wherever there is any natural vegetation still present? Maybe some kind of tall growing yucca, perhaps?

They are starting over from the bottom and you will have to wait however long it takes for them to recover their original stature just to get back to where you started. And if it got that cold there once... Because this was intended as an architectural feature (living screen) I think you should jerk them and start over with another choice. One that will not freeze down should the same conditions occur again while you are still living there. Conditions that may happen again anytime, because killer winters don't come on a predictable schedule. And sometimes come in sets, with only one or a few years between each episode.