It really does depend on the dog, and the cat's, temperaments and natures. On the whole, retrievers are friendly social animals but there are the exceptions to the rule. How old is the dog? If you and your cats are only going to your mums for a visit, I would keep your cats and the dog seperate. If this is not possible, then introductions must be made very slowly and carefully.
I have 4 cats and 2 dogs, who all get on great.