How does looking at dimensions affirm that metric system was used?
> They live in respectable houses, and host meals with respectable friends. They eat well. They travel for holidays, by plane, all over the Earth.
The OP tells as if this is a good thing. However this is the scariest parts of all. Because who knows these people can as well be the next presidents.
> As a Flat-Earther, having your theory rejected only re-confirms the Illuminati’s brainwashing campaign.
A good point, which even most of the political strategists DO NOT implement. "Pushing extreme ideas does not swing votes."
Conclusion: OP seems like he has given up on trying to come up with good ideas to deal with fallacies of his parents. This might seem cute at first, but there isn't a sense of realization that this might be very harmful to the society as a whole.