Ooo, :clap: I buy to collect too, but don't have many. I go for briefs though. What do you have? Whereas for own use, I wear a mix of briefs and boxer briefs, mostly the cheaper ones, so that won't heart pain when they get torn or worn out.
Since you're only the uncle, it will be your responsibility to let his parents know about this as the kid is still schooling. Maybe you don't want to be too direct and want to test water first, you can try by hinting with questions like if they know their son is .......what are they going to do about it. Leave the problem (if you consider that it is) to his parents to handle, afterall its their responsibility on the kids upbringing.