You need to start now by introducing the dogs to the realities of a baby. Dogs learn through their senses first – scent, sound and sight.
Scent – baby powder, baby oil, baby lotion, diaper rash cream, formula, etc.
Sounds – babies cry.
Sight – babies move and wiggle.
So, here’s what I suggest. Get yourself a baby DOLL. One that moves (waves arms), makes noise (cries) and feels as lifelike as possible. Start treating that doll like a REAL baby. Carry it around, talk to it, put lotion and powder on it. Teach the dogs how to behave around you when you are carrying the baby.
Also ask to tape record a friends baby crying. Put that in the crib where the baby will sleep. A couple times a day put the baby in the crib and start the tape. Let the dogs hear it crying.
Do everything you would do with a real baby with the doll. Even ‘borrow’ some used diapers from friends so the dogs can see and smell what changing a baby means.
If you keep this up then bringing the real baby home should be a lot less stressful for the dogs.
Also, have a blanket that you use on the doll all the time. Don’t wash it the month before you are due – you want it to really smell like you and that doll. When you go to the hospital to give birth – bring that blanket with. When you are ready to come home with the baby use that blanket to wrap them up. The dogs already associate that smell with the doll.