I can’t contact them for professional reasons I’m afraid, hence the thought on here.
I guess I could make up a name. 
Anyway it is offensive to all women to call our existence 'transphobic'
^ that puts this whole debate in a nutshell. Beautifully succinct!
If you’re contacting them, maybe worth saying that even if they did put a 12 year old in charge of their Twitter account, that’s not the point- Their tweeter only reflected RSB’s existing corporate equality and diversity policy which is ‘gender’ not ‘sex’. We couldn’t expect anyone from RSB to tweet otherwise with that policy.
It’s a ludicrous and dangerous position for a professional biologists association to get into, but they’ve done it to themselves and they need to sort that out.