Over growth of ferns
Thanks for the question.
Let me see if I understand things correctly. You currently have this large area of ferns in a garden next to a fence. They are spreading out of control. It appears that you do not want to eliminate them completely but just remove some. Some of those that you remove you would like to transplant elsewhere. I will respond with these assumptions.
The fronds on your ferns should soon, if not already, start to turn brown and die back. While it may be tempting to “tidy things up” by removing this foliage now (fall 2019), avoid doing this. The bases of your ferns (called the “crowns”) need to be protected in order to survive the impending winter. The brown fern fronds will do this. It wouldn’t hurt to cover these crowns with two or three inches of wood mulch at this time. Water the ferns well until the ground freezes. Early next spring (2020) remove the dead and decaying foliage. Then do your thinning by digging up those ferns you want to remove. Some or all of these can be transplanted. The following will give you information on these and other related points: