yes repot into bigger pots. you can do it now as they are in pots. you don't say how big the camellias are but I would certainly go for 12" pots with fresh ericaceous compost.
you will get the odd yellowing leaves through out the year this is normal.
don't let them dry out.

Thank you very much- I’ll get some ericaceous compost and repot them. Will they need any feeding or is it too late too late in the year for that ? I’m very relieved the yellow leaves are normal

the compost will have enough food in it for the autumn / winter. It wont be using much. mid spring early summer give it a light feed with either a general all purpose food or one designed for camellias.