Hi, some pruning and plant preparation advice please.

I just got my delivery of 10 x 15gal column podocarpus gracilior trees.

They will be planted in raised planters against a concrete wall, with the objective to grow into a solid hedge, and tall above the wall to provide some privacy from the neighbor's second story windows.

Most of the trees have a single stem/trunk, but a couple of the trees have a main trunk, and one or more smaller stems.

Here are some pictures:
https://www.dropbox.com/sc/1ssakx1m4d7vuey/AADLWxSFRtQcHaGY6rdlCUCTa

Should I cut the smaller stems so only one main trunk grows, or should I leave them and just prune them short so they don't stick out of the hedge formation?

Thanks
Pieter