Get them out of that incredibly unsuitable compost and have a look at the roots and you'll be able to assess whether the problem is rot much more easily. If the problem is sunburn, they'll be okay in the long term - they'll shed those leaves and look fresh and new eventually.

It is best to acclimatized plants to new growing condition. Even sun lovers needs to be acclmatized, since it is difficult to know what kind of sunlight they were in before you got them. They will burn, often even if they were in good liight in a GH/store. Direct outdoors sunlight is much stronger than indoors.

Repotting into better mix is good idea. Pots do nt need huge. These plants have usually longer roots, so do not use shallow pot or dish.