I'm not sure how it works but certainly the guests should just cancel their room bookings as this usually only requires 24 hours notice.
WRT to banqueting room, how would you feel if they rang you and said they wanted to cancel for some reason and want to refund your deposit and go along the lines of your 4th point "No contracts signed, no terms and conditions supplied to couple at time of booking", I'm sure you'd be hopping mad.
If it was me I try to meet them half way and offer them some sort of deposit and let the guests sort out their own bookings.