I also had 5 kids, 5 in 10 years, so I have lived and understand your life. Your dog at 9 months takes almost as much time, interaction and training as a human two year old. With another baby on the way, and the sleep deprivation that goes with a baby, the work load that goes in running your home, I would seriously considered rehoming your dog.
I didn't get a dog until my youngest was 6 years old. What our family did was foster puppies and dogs from our local shelter. (We stopped counting the number of foster dogs we'd had after we'd had 50). We had a break from shelter dogs. We gave guide dogs that needed a break in their training holidays at our house. It was good experience for the guide dogs living with all the children, and the dogs were trained so it was easy for the family. We had our 'dog fix', but we also had breaks between dogs.