Can cats and dogs get along?

I have two cats aged three years old, they are friendly and tolerate / befriend other cats. My sister has just bought a puppy and although the cats are bigger than the dog they are totally petrified of it and are now not talking to me! They stay outside all the time and only come in to have something to eat. How can I get the cats to like or at least tolerate the dog and also get them to start talking to me again so we can have a harmonious household once more! Thanks for your help!