I will need more information to comment properly. If he is improving with medications then I will suggest to keep the medications as it is.
Sizodon 0.5 mg can be considered to be tried and tapered off under supervision of a psychiatrist, as it is the lowest dose of the medication and I am not able to understand the reason for the medications ith the current available information.
As for fluoxetine he is on good dose and should continue and if he has not had any side effects till now he is less likely to develop any now. Although a watch should be kept on him because some side effects can come at long term but they are not so common. And in any case a treatment period of 6 months to 1 year is minimum for anxiety and depression.
Next Steps
if you still are not sure then you should consult a psychiatrist for detailed explanation.
Health Tips
if you feel that some side effects is happening you must get him checked by a psychiatrist so that it can be clarified whether it is due to drug or not.
do not in any case stop the medications suddenly as there might be rebound phenomenon with medications and his condition may get worse. always dot he tapering under supervision of psychiatrist