First of all, thank you for replying directly to my question. I like keeping things simple - none of the 'tying yourself up in knots' you mentioned earlier.
Because this is basically a very simple issue: science says that there are only two sexes, and you can't change sex. If I've got it right, science also says that all the trillions of cells in our bodies have the chromosomes which decide our sex, so it's not like being male or being female is located on any one part of our bodies or our brains.
Keeping things simple again, this is why men presenting as women is so problematic: it is based on the false belief that being a man or a woman depends on outward appearance. That's just not true. Plus or minus bodyparts, your friends are still as male as the day they were born.
As I've said before, I think it would be so much better if gender-questioning young people were told these facts directly and honestly : there's nothing you can do to change sex, so don't cut parts of your perfectly healthy body off, don't have non-functioning extra parts added to your perfectly healthy body, don't submit your perfectly healthy body to a fuck tonne of estrogen or testosterone, and don't condemn your adult self to living in some kind of in-between zone;. now what can we do to help you accept yourself as you actually are and live your best life without fighting against your perfectly healthy body.
If anything should change it's not young bodies, it's the strict stereotypes of what 'a man' or 'a woman' is or looks like which seem to make some people like your friends think there's something wrong about their bodies, and subject their poor bodies to dangerous surgery and a lifetime of medication that will never achieve what they they've been told they can achieve: changing sex.
Note I'm not even going near the social and ethical issues of men claiming to be women - as someone who had a very very difficult time as a gender-non-conforming child, I'm just sticking to the basics, and hoping children like me, and your trans friends, can be helped to love themselves as they are, and are not sold dangerous and false claims that they can transition into something they are not.
Again, thank you for engaging with my question. We both care about our friends and want what's best for them, but where we differ is that I wouldn't want any of my friends to damage their bodies with surgery and pharmaceuticals to try to achieve the unachievable.