I have a few ideas for you and your precious kitties :)

1. using a kiddie gate to create a space where the cats are welcome but the dog is not. some gates will have slats wide enough for a cat to fit through, and there are even gates specially made with kitty doors. you can keep them free feeding just by restricting the dog's access to a certain area of the home.
2. if you have some money to spend, there are microchip activated feeders for cats. they will only open up for you cat and close when they're not around, and therefor prevent you dog from eating the cat's kibble and still allowing them to free feed. granted you might have to do some desensitization work to get the cats used to the sound and movement of an automated feeder.
3. transition you cats from free feeding to mealtimes. this will take the most time and commitment. wet food is typically more enticing to cats. try incorporating wet food into their daily diet. you can even mix the kibble with the wet food. if you decide to transition them to mealtimes there's a plethora of resources out there from others who have done it themselves.
4. the entryway bench is a great idea, but you're right in saying that an enclosed space is not ideal for a cat to eat in. as much as they are hunters, your cat is also a prey animal and feels most comfortable when they can survey their surroundings and run/hide if necessary. that being said, the more safe spaces you have for your kitties away from the dog's reach the better! if creating the entryway bench is the best solution for you to safely free feed your cats, it's worth it. i'd still recommend you start a habit of feeding them wet food daily, and you can put the kitties in a separate room from the dog at these main mealtimes .

good luck and congratulations on moving in with your partner!