I know almost nothing about clivias and am just going by what worked for me. I started several clivia seeds in a pot and divided them into individual containers when they were at the 2 leaf stage but only a couple inches tall. If I recall correctly it was mainly one really long root on each plant and was pretty easy to separate. Yours are much taller then mine were and probably have a better developed root system so they might not be as easy to tease apart but I think the sooner the better because it won't get any easier. I could be way off base and hopefully someone with a bit more knowledge about clivias will chime in. Good luck.
Karyn