This was roughly the early cosmology of Judaism, but even by Jesus’s time was being abandoned. For example, the Greeks and Romans were familiar enough with both lunar eclipses and the Earth being round that the generally accepted explanation for lunar eclipses was that the Earth was eclipsing the sun and casting a shadow on the moon, which we know was popular because in De Rerum Natura Lucretius appeals to keep more of an open mind as that might not be the only explanation (meaning it was commonly enough endorsed that it was nearly considered the sole explanation in Lucretius’s circles).

This may even connect to the description of the “crucifixion darkness” in the earliest copies of Luke where it is explained as being caused by the sun being eclipsed. That language is changed in later versions, and the language of ‘eclipse’ was criticized by early church commentators given that solar eclipses were known to be impossible on a full moon (such as Passover) and only last around 8 minutes.

But what’s often overlooked was that being written after 50 CE, visible nighttime lunar eclipses whose previous Saros cycle eclipses were during the daytime in the 30s CE would have been able to be trivially calculated by astronomers of the time.

Lunar eclipses take 3 hours, and have a 1 in 6 chance of occurring on Passover. We even know there was a daytime lunar eclipse on Passover of 33 CE, whose subsequent Saros cycle eclipse was visible in both Judea and Greece before any of the Synoptic gospels were written.

So not only would some of the anti-firmament cosmology known by the era of the New Testament, it’s quite possible that there was even originally text reflecting both knowledge the earth was round and that lunar eclipses are caused by the earth eclipsing the sun, but it may have been subsequently removed because later editors failed to realize the event was not an eyewitness testimony but a calculated celestial event and thus dismissed it as erroneously describing an impossible solar eclipse.

TL;DR: Your family member is nearly going pre-NT with the commitment to that cosmology there.