Cats and dogs are so different and you have thought about this so carefully. Cats are not going to fall victim to their instincts with a human baby the way a dog might. Even a small dog could take on a baby and win. A cat is going to see a baby as too big to have a go at. Keep an eye on things, especially as baby gets mobile!! If the baby is asleep or you are hanging the washing out, just don't take a chance. Close doors and use the baby monitor. There will be times when you are soooooo tired you will think, "Just for a couple of seconds they will be fine." The risk is not worth the couple of seconds, more because babies change from day to day and when they couldn't grab the cat yesterday they can today than the cat hurting the baby.
I can almost garuntee that once baby is here and animals and baby have no conflicts then your Mum, eventually ( probably not 'till the baby is six years old!) will be saying that it was lucky you had THOSE animals. If you are planning a large family it will be the same every time!
My mother still thinks it is a miracle that my kids (10 and 6) have survived!