Eric,
What I've suggested here is another way of plumbing 2 electric vac motors.
If, for some reason, you don't think it will work, or that it is not a correct way to install 2 vac motors in an electric configuration, or you don't like it called series, you are certainly entitled to your opinion. I'll call it parallel lift configuration, if you think that sounds better.
I've done extensive testing with many different electric vacuum motor configurations over the past 25 years, so that's where my tip (comment) came from.