Hard to tell from photos, but pots look too small. Could be uneven watering and low humidity causing the problem. You are keeping these outdoors during the growing season, aren't you?

Thanks!

No, they are all indoors, i live in Sweden so they dont get a whole lot of light. Should i try to cover them in some plastic to keep the humidity higher?

All the best! / J

Here are some suggestions:

http://homeguides.sfgate.com/camellia-leaves-turning-brown-67700.html

http://www.camforest.com/category_s/70.htm

http://homeguides.sfgate.com/grow-camellia-sinensis-indoors-66238.html

Camellias don't generally make good indoor plants, but one thing I would suggest is that you don't let your plants dry out between waterings. Also camellias don't want to be warm in the winter so if you have a well-lit, unheated room that will mimic winter conditions without exposing the plant to freezing temps, that may also help. Well-lit may involve some sort of artificial grow-light, given your latitude.

Good luck,

Virginia