I have both of the tree ferns and palm you mention ( no olive tree).
Cyathea australis is I believe as hardy as Dicksonia Antarctica
All three appear quite happy outside in winter (West Yorkshire ).
The tree ferns loose their fronds with heavy frost but with a small degree
of protection (fleece ) the fronds will survive at least another year. The
old darker green fronds make a good contrast with the new ones. At the least
protect the crown with a handful of straw or leaves.
My Phoenix canariensis planted in a windy well drained soil is as tough as
old boots and looses the odd lower branches only
How old/established are your ferns?
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