Ok, I have finished my experimenting on my invisible Grandbaby Sim issue. I would like to share what I discovered so that it might offer answers to others who may be having the same or similar issues.
First, I had "testingcheatsenabled true" and "moveObjects on" cheats on. I tried to move the Sim family out of their house but could not because the Sim baby was glitched. I tried the "resetSim" option several times which did not work.
I could not bulldoze the house because she was stuck inside of it.
I went back into live mode and zoomed in on their house. I "shift + clicked" on their lot and clicked "build on this lot". I then took this house apart piece by piece with the hammer/mallet tool. I worked my way from top to bottom including the entire landscape. I deleted every single thing until only 1 item remained. I found that the glitched item was a floor panel just inside the front door. I could not delete it because that is what the invisible Simbaby was sitting on.
As a last resort, I had to "shift + click" on the adult Sims and click "Trigger Age Progression" until they were ghosts. Once they were gone, their children were gone too, not dead - just gone.
I then went back into edit town and bulldozed the lot to be sure it was clean and free. I put my saved copy of the family and their house back in place and it was all good. The Grandbaby was back and I was happy.
But, there is a downside as well. My Sim daughter that I had to kill off is considered dead in the family tree. Her new "clone" and family are back into the town, but she and her family members are only considered townies now. There is no family identity/connection between her and her Father, Mother and siblings.
I deleted her gravestone and her husbands and it doesn't change anything. She is still just a stranger to her parents and siblings.
Thanks to everybody who responded to my posts and for your advise!
I hope this information will be helpful to someone else. Good Luck!