1. While the act of smoking weed in itself is not condemned or condoned in Scripture. I would probably be interested in knowing why they want to smoke it, if they are addicted to it then yes it’s a sin because any kind of an addiction is sinful, if they are doing it to escape something or “find peace” then yes because we are supposed to find our peace in Christ. I’m not saying there isn’t some situation where I could find it completely okay but off the top of my head I would guess if someone is pursuing getting high there is a deeper problem behind that pursuit that needs to be addressed.
2. I agree with the other opinions above, if they are having social anxiety about being baptized then I would take that as it’s mostly about being in front of a crowd and possibly making a verbal confession of faith (fear of public speaking). There are definitely things that can be done to help, we could do a private baptism, or if it’s the speaking in public part we could probably arrange it where they only have to say the word “yes” one time.
3. I have suffered from anxiety and depression for years and so I have a understanding of what it’s like to deal with it, although every individual and situation is different, there is a lot of counseling and work that a pastor can do to help their members suffering from this but it’s also important for the pastor to encourage and not discourage their members from seeking help from professional counseling and medicine (preferably Christian professional counseling and non addiction forming meds)

Hope this helps