I requested a microfilm record of Ottilie Meyr's christining today. It should arrive at the BYU FHL in 3-4 weeks.
I'll begin by going to the census records I've already found Gustav on and sourcing as much data for the family as I can.
There are 14 children for Gustav and Paulina listed in the 1920 census but only 12 listed on NFS.
My guess is that Ottilie Lina Meyr (listed on NFS FT) is not a child of this couple and that William, Walter, and Otto Arthur are. Now I will search for birth certificates and other information to verify or refute this hypothesis.
Perhaps Ottilie is the daughter listed on the 1910 census as Lucie M? Ottilie is probably a real daughter because Grandpa Meyr's username added her.