What are these grasses and can I chop them back?

[DarthWeeder]

Photos don’t do justice to how tall they are, the seconds one is 6ft and they are taking over!

Cordylines/formiums. Cut the leaf stems from the base if you want to shape it.

It’s Phormium tenax, they grow enormous! You can cut off any dead foliage at the bottom, but they do grow large.