That was an Ideal post IMHO. You made your points persuasively and challenged his points directly.
Seasonality doesn't work with a flat earth, but works out just fine with a rotating sphere. Southern hemisphere got inverted seasons from the Nothern. When we got +34°C in Stockholm it's snowing in south Argentina. I traveled to the north of Sweden a couple of weeks ago, above the Polar Circle. There you have sunshine 24/7. All the stuff mentioned above doesn't work with a flat earth but works just fine with a rotating sphere.
and so on and so forth ...
Montana Mel and Silver66
I hope you and your relatives have a recovery soon.