What about a "please use English in the usual way to avoid causing offence" policy?
Why does GC offence not count?
We shouldn't need a special safeguarding reason not to have to play the preferred pronouns game. It's a question of freedom of belief.
GC beliefs are protected, as GR is, but this whole discussion started because we don't yet know whether GII - which is the issue here - is a protected belief/set of beliefs.
A reasonable workplace policy about pronouns in my eyes would be: ask, but colleagues can say no. Wear your pronoun earrings or badge and others can ignore or take note.
A compromise means both sides have to give up something. The GC/Sex realist staff are already compromising by agreeing to call a man by a female name, or vice versa. Where is the compromise from the GII side?
You cannot impose your personal beliefs on others - not even by way of taking offence at words which are only offensive because of your beliefs.
As a pp said, courts are starting to allow the parties to use correct sex pronouns.
Management should not throw its weight entirely behind the pronoun-havers.
This is not even like insisting people using the word "bathroom" instead of "toilet" because the employer is American, because at least the two words mean the same thing in the different forms of English.
Forcing others to use wrong-sex or neo-pronouns is imposing a belief system.