Could you maybe talk to your sisters about how you feel in person? I can understand why you wouldn't want your mum there if you don't get on. It's your hen do and you should enjoy it.
or else suggest a get together like afternoon tea or something just for the ladies in your family including mum? That way it's only an hour or so and you can hopefully get your sisters back on board but yes otherwise just ask your sisters why they're not getting involved in hen chat... they might be put out that you've got your friends in charge of organising it when they felt it would be their job? In which case you could say you really want them to organise something specific for it like tshirts or party bags or a nice meal whatever the hen do involves x
[edited to remove details. Thanks for the advice.]