Yes, the "green" "red-ear" tortoise need sunlight, as sunlight provides them with enough vitamin D. A proper way is to give them UV light so that they will be healthier.
There's a vet at Tai Wai which is good for the tortoises. I just brought my sick tortoises there as they are sick and now they are having injections..... at least I feel the vet there possesses good knowledge on tortoises. There are far too many vets around but seldom do they have good knowledge on tortoises.
Also, remember to give the tortoises some vegetables to eat. Just tease the vegetables into tiny pieces and the tortoises might eat. It's good for their health!!!
continue to use the medicine for one or two days until the tortoise is totally recovered. Sometimes, they open for a while and close most of the time when they are recovering, please check.
Also, remember to expose them to the sunshine more.