Hi welcome to YT!
I live in Florida like your mom does. Glad its not snowing where I am. Hope your mom decides to join too. Well she is brave to have the rotties too with the yorkie. I know they probably woudn't hurt a soul, but I'm just paranoid with my girls LOL!!
Maybe try a harness with your baby and just leave it on her for periods at a time and gradually introduce the leash (attached to the harness) easier on their little necks. Personally my girls aren't that familiar with their harnesses as they get toted most everywhere!!! Can you say SPOILED!
Can I blame that on my daughters???
Anyways good luck with your new baby. I think you will find this site to be most informative!