Introducing new cats to the dog (or vice versa!)

[madamy]

We have a fairly lively 10 year old, small/medium dog (rescue, mixed breed) and a relative is looking to home 2 young cats (not kittens). We've previously had a cat who was elderly when we got the dog and she definitely was the boss - he kept out of her way!
I'm considering taking the cats (kids are 15 and 17) but wondered how ddog might be now he'll be the boss. He's super friendly and inquisitive, but does love chasing the resident squirrels (although is scared of our hens!). Also, how to ensure the cats have a safe place to go to etc.
Has anyone done this successfully?

Don't want to completely put you off but it's been a disaster here, dog won't come upstairs and cat won't go downstairs! Both older.

We acquired the cat (not my choice) but sort of had to take her in and the dog is here 50% of the time shared custody!

We manage but I would definitely suggest a trial run