I'm so sorry for your losses. We don't get very cold weather here in Ireland either, but in the month before xmas it went down well below freezing for over a week on 2 occasions. I lost 3 birds myself.
Throw tons of straw into your rabbit hutches, they can burrow into it and huddle together.
Make sure all indoor areas are dry and draft-free.
Put a layer of vaseline on the combs of birds with large single combs, this will help protect against frostbite. If you do it at bedtime they won't complain or struggle much.
Feed them something warm a hour before bedtime. Some people make oatmeal for their chickens. I just put mixed grains in a dish and poured a bit of warm water over it.
To help keep waterers from freezing over so quickly, try using a metal dish, placing it over a square of bricks, place a lit tealight in the centre of the brick square.
Put some extra vitamins in the water too, it won't hurt.
All the best to you during the rest of the wintry weather.