What you need to do is to force them to explicitly own the misogyny of the position they are advocating. This is for the benefit of WEP members in the room: they need to see Brewer and co say out loud that they believe women and girls have no right to safety and privacy from men.
So questions like 'What about predatory men taking advantage of this law?' won't cut it. That hasn't got us far in this debate, because it just gets hand-waved away with, 'No evidence of this happening, no reason to exclude 'trans women' because of what 'cis men' might do' (as if there is any difference between 'trans women' and 'cis men' except self-declaration of a feeling-state).
Instead, ask a question that forces them to be upfront about what they are advocating. I like what @Materialist said in another thread. She said she asks people 'simple, clarifying' questions like:
Do teenage girls have the right not to be naked in front of male eyes? The right not to shower next to a penis?
Yes or no answers only.
Very few people will argue that a girl does not have that right, but if they do well, at that point I’d know exactly what they were.
Brewer and co, of course, will argue that a girl does not have that right. In fact that's the entire point of what they are working towards: they are working to ensure that no woman or girl, anywhere, no matter how vulnerable a state she is in (in prison, in a refuge, in the shower), has the right to be free from the presence of males.
But others in the room will not have grasped that that is actually what they are advocating for. Because it's all couched in the language of 'oppressed trans people, inclusion, etc'. They will be shocked to hear it said out loud:
'So, just to clarify, you believe that girls in public change rooms should be forced to undress in the presence of males, and to be exposed to penises in public facilities?'
And it will wake them up as to what all this fuzzy talk about 'inclusion' really means.