When you re-pot, you might want to line that/those pots with a garbage bag, with large holes cut out on the bottom so that the pot still drains. That should easily slip out. When I grew my ferns (I only grow stags now), I would remove them, cut off all the top growth, and then use a sharp shovel to separate the root ball for re-potting. Depending on the original pot size, I would divide the plants into 2 or 4 segments.
