J.,
I have three kids and 2 dogs. My dogs never really bothered with the kids. Someone told me that when the baby was born, take home the first cap that they ut on them, let the pets smell that, so that they are familiar with the smell of the baby. When I came home from the hospital put the babies on the floor in their carseats and let the dogs sniff around them. them sniffed them and then went the other way. One thing I can tell you from experience is to let someone else carry the babies into the house for the first time. If your dogs are anything like mine they were more excited to see me that they were to see the babies.
As far as cats, I have never owned any. the only suggestion that I do have is to try to keep them out of the nursery. I know that cats can jump over gates, but a frient of mine had a great idea. She had two cats when her son was born and she got really mad one night when she went to put the baby down and had to chase the cats out of the crib. She had her husband go to HOme Depot the next day and figure out what to do to keep the cats out of the bedroom. he purchased a very nice looking wooden screen porch door. he painted the door to match the bedroom and he bought letters and put the baby's name on it. It really looked neat and it kept the cats and dog out and they were still able to hear the baby and the room didn't have to be closed up. It might sound weird, but if you or anyone you know are creative you could really have fun with this. Good Luck!!
C.