How gentle are you?

If you are very careful you can tease the roots apart gently and repot them now. I would wait until they were large enough to be hardy but not so large that roots have gotten very thick and twisted together. Couple good flushes of nice healthy leaves.

Remember to handle these by the leaves not the stem- they have lots of leaves but if you crush the stem you are done. And don't bury them too deeply!

Keep them in bright indirect light for a week or so after the repot to give them some time to settle.

Thanks for advise, cearbhaill. The seedlings currently have just three-four leaves. But I am afraid their roots may have already reached the bottom of the pot, and that perhaps they are not comfortable in this small pot. But I am afraid more of damaging the tiny seedlings. Is it O.K if I leave them in this pot until autumn???