First of all you need to unmistify pshychiatric diseases in yourself so you can fully comprehend what is happening to him.
This diseases are like many other biochemical malfunctons of human body. I like to compare it with diabetes, because is a very common disease. So a diabetic patient has an altered metabolism where he or she can´t transform sugar efficiently, and thus it trends to buid up on blood. A normal person and a diabetic can eat the same piece of cake, but one will use it efficiently and the other will take ages for his glucose level to normalize. A depression is very similar, they have a problem with chemicals on the neurons that control emotions. So if a healthy person and a depression patient suffer something stressfull (ex. rejection from a job position they were eager to obtain) they react diferently. The normal patient will likely become sab but will efficiently react and move on, but the depressio patient will not, because his neurons can´t correct the chemical inbalance due to chemical failure. The depression will worsen, feelings of helplessness will rise, etc...
Unfortunatelly there are hundreds of different types of neurons some of those use similar chemical than those involved in depression. No drug if perfectly specific to target only the affectes one, so secondary effected are inevitable. Like drowsiness, low libido, increased or lowered apetite, headaches. Every drug is different so some patients need to take multiple trials until they find the perfect one.
Actual mainstream treatment for depression and anxiety requieres not only drus but also therapy. There are multiple scholls and techniques to achive remision of the disease. There is no way to now what will actually work best for him.
If you love him you should aknowledge that he will need treatment allways, and support. It is a good sign that he is aware of his problem.
Also realize that there is huge ignorance about mental diseases. So you will always face comments like those of your family.
Your path will be a difficult one. And it will highly depend of his commitment to treatment.