A lot of people seem to conclude that Sherlock’s queen and mother comments towards Mycroft in ASiB are references to his sexuality. I think that short of getting Mycroft to voluntarily fill out a “I self-identify my sexuality as X” questionnaire on screen you can’t really make any assumptions (though fic was basically invented to allow for the exercise of harmless speculation), but I do just want to pick up on the mother comment.
In the UK, “I’ll be mother” is just another way of saying “I’ll pour the tea” - it’s nothing to do with sexuality. (Oh yes by the way, this is more about tea from me.) The Oxford English Dictionary lists being mother in the sense of serving out food or drink, and has the first specific-to-tea entry dating back to 1934: “‘Shall I be mother?’, said Ella, and started to pour out the tea.”
Sherlock’s comment about “a whole childhood in a nutshell” seems to me to be two-pronged. First, referring to Mycroft adopting the responsibility for pouring the tea without checking to see if anyone else wanted to do it, just assuming the I’m-in-charge role without being invited. This particularly applies when you consider that he doesn’t actually work at the Palace (frequent visitor maybe, but the office we’ve seen isn’t there) so the “host” would be Harry; you would generally look to the host to take on the tea pouring. The second prong is in the sense of “to mother” being synonymous with fussing and over protectiveness - Sherlock has no doubt been the subject of a lot of mothering from his constantly worrying CCTV-controlling big brother.
So I don’t think it was anything to do with sexuality. It was just that the simple act of volunteering to pour tea for everyone is viewed, through Sherlock’s complicated history with Mycroft, as yet another example of his overbearing brother constantly fussing over him and being controlling.
I’d have just left the ungrateful so-and-so to pour his own damn tea.