Answer: Based on your description I think you purchased two plants trained as standards grown on a single stem or "trunk". Pruning would be done only to trim back the branches by about half or possibly two thirds.
Do not cut past the top of the trunk, however, and do not cut it off at the ground. Remove any shoots or leaves that might try to grow on the bottom portion of the trunk as these would divert energy away from the decorative top growth and could eventually cause the tree form to be lost.
You might consider repotting them this spring. Feed them with a water soluble fertilizer once they begin to grow again. Keep them in the brightest possible light and gradually acclimate them to the outdoors when daytime temperatures moderate into the 50's. (Bring them indoors at night until nights are reliably over 50 degrees.)
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