Just cut the roots as they emerge from the bottom of the pot and repot as normal,maybe raise the pots off the ground a little using pot feet or bricks this time.I would water them with fish emulsion after repotting.I doubt you will harm them by doing this.

I repotted my Clivia a few weeks ago, and now have new flowers, so no harm was done in repotting it.

Don"t over water - be sure there is good drainage or they can rot out.