It can be relatively easy, if either the cats are kittens or the dog is a puppy. If they are both grown up and set in their ways it may be more interesting. Our first Lab was a 4 yr old rescue from the Humane Society. We took her over to the Cat side and watched her reaction to the cats and kittens. She was fine with both, and we ended up going home with two kittens and a 4 yr old Lab.
I had 2 5 year old cats when I introduced my puppy into the family - they were not impressed with the new addition . Some key points to introducing a puppy to resident cats :- Introduce puppy crzte/pen/bed into location a good week or two before puppy arrives to allow cat/s to get used to it. If possible bring home a tieel/blanket with puppy smell on it to put in crate before puppy arrives home as it helps the transition as the cat/s already have the smell. All interaction are at the cat/s discretion and puppy should be on lead and preferably through a barrier initially. Cats are provided with a safe, puppy free environment to eat, sleep and relax. With mine their food and water were placed upstairs and their litter tray placed in the bathroom as well. A stair gate was used to prevent puppy going upstairs while allowing the cats access. The puppy is never allowed to chase or bark at the cat/s - reward for calmness around the cat/s I used Feliway spray as well to help reduce stress for the cats. Patience and time to allow the cat/s and puppy get to know each other without any pressure from humans
I have a 13 year old cat who is very much set in her ways, I had a 5 year old cat and a 1 year old cat previously but the 13 year old didn’t get on at all with them, so we had to separate. So it was a huge risk when my assistance dog came along being just under 2 years old. Yes well trained but still is a dog and has mad moments. Luckily they get on really well, after the third day, she started to venture out to meet my dog and accept him slowly. No problems. This way done through many ways. A week effort I got my dog I plugged a natural diffuser which lasted 8weeks in total, my cat got some calming benefit before my dog arrived but then my dog was calm from the start and helped him settle in easier too. Previous to my dog arriving I had his bed laid down so the cat could sniff at it and even lay in it and get used to his scent, and I gave something with her scent on to the assistance dog trainer to give to my dog until he came to me. From the first day with me, they had own toys, but would have two toys suitable for playing for cat and dog, these would alternate between them so the scent would alternate between them, and encourage play over the coming weeks I noticed. The first couple nights mycat slept in her usual place and the dog was tethered on a semi long lead so he learnt where he should be over night while I slept and not to disturb the cat while I wasn’t able to watch. He has to sleep in my room due to being an assistance dog, but I assume for a pet dog they would train to sleep in any room? I feed my dog in a separate room too as he will shoot towards my cats food even when she is there, and as good as his training is he won’t leave her food. And we don’t want this to break their connection they have now, so possibly feed in separate rooms and don’t leave cat food down all down or your dog will just gooble it. https://www.purina.co.uk/dogs/getti...g-your-dog/introducing-your-dog-to-other-pets Gives a few ideas too