First, congrats on your baby! And don't apologize! Pets.ca is a great forum, with lots of people and varying experience - you've come to a great place for help.
It's very normal for chihuahua's to be possessive. A lot of dogs ARE possessive and protective of their family members, but the chihuahua breed as I'm sure you know, is known for how attached they become to their owner.
New baby's always upset the home hiearchy, but it does not have to be a stressful experience for you or your dogs. I really suggest consulting a trainer in your area to come to your home and give you some handy tips and advice, to meet your dogs, assess them, and show you some great ways to introduce your baby safely to them when they come home.
When my daughter was born, we made sure that her blanket came into the house before she did so my parents dogs could be 'introduced' to her that way. By the next day, they were used to her scent and her presence wasn't such a shock to them.
Many dogs handle new babys just fine - but the odd one can be stressed by the crying and the sudden loss of attention. It's important to show your dogs one-on-one attention after your baby is born, but speaking from experience, the first few weeks will most likely be a little bit crazy for you - and obviously your attention will be focused on your baby.
If there's another family member around that can play with your dogs, take them for walks, etc. that will help matters; but if you personally can ensure that you set aside time each day to give them lots of TLC, that will help.
One tip I can give you is to start sitting down with a baby doll throughout your day. If your dogs come over and start climbing on you while you're doing this, make sure that they know that when you are holding something they cannot do so. Once they're sitting calmly at your feet or beside you as you hold the baby, make a big show of putting the doll aside, and at that time - give your dogs attention and praise.
And again, the best advice I can give is to find a reputable trainer in your area who can come to your house before and after the baby is born to help you work through this.
