This is your treatment and you should feel free to voice your opinions and concerns about any part of it.

I can't speak for all psychiatrists or your psychiatrist, but the one I saw liked to prescribe a medication that had helped a family member. He though that it was likely that the med would work similarly. I think also if a patient has a high opinion of a med and has expectations that it will work well, that increases the possibility of success.
Similarly the psychiatrist will want to know about family members' reactions to dertain meds. It will be important for him to know this.

Sure, tell him you have read about Celexa and you would like to try it. He may have other suggestions, as he is a specialist in medications.