Dear Nephew has made it clear in his own way, that he is too hot for tights as well as the trousers.
Nursery seems to also recognise that, else the wouldn't be removing the tights whilst he was in their care.
The fact that he's a boy is irrelevant, only his feelings of discomfort are.
If it was a matter of him feeling distress over wearing clothing that was causing comment, that should be addressed too.
I could cry for this little kid... if I was told I HAD to wear clothing that made me feel hot, and I could not communicate that to whoever was dressing me, I would consider that to be abusing my feelings, even if my carer acted with best intentions.
The FC in the op HAS been asked to refrain from dressing the child in the tights.
The FC should've complied with the child's mothers request.
My goodness, for mum to be so ill that she knows that she could die, and that her dear child is not being listened to, nor the child's advocating aunt, must surely be making her feel so impotent in her child's future care.
OP, I no little about how the FC/SW system operates, but there has to be a way to educate the FC to work WITH the mother and possibly you too as his advocating aunt.
Also from your post, it's not only the tights issue that is upsetting his mum.
The pp that seem to believe that the mum should be grateful that an FC is available, therefore shouldn't moan, suck.
There are plenty of pp that raise the roof if their mil go against their wishes with the grandkids.....
OP, be as strong as you can be, both the uncomfortable child and the child's mother need you to be that lion.
I know you have your own issues, and I really feel for you... must be more than difficult and distressing.
I wish all of you the best possible outcome.
Personally, I'd like to dress the FC up in as many layers as possible, and tie her hands up, then turn the heating up to t-shirt level.
Tell her it's because I'm concerned for her, as I feel too cold....
Gee, when I have a hot menopause flash, I can't wait to rip my layers off.
I'd literally go mad if I couldn't get them off.
Big hugs x