NKJV: Josh 24: 1 Then Joshua gathered all the tribes of Israel to Shechem and called for the elders of Israel, for their heads, for their judges, and for their officers; and they presented themselves before God. 2 And Joshua said to all the people, "Thus says the Lord God of Israel: 'Your fathers, including Terah, the father of Abraham and the father of Nahor, dwelt on the other side of the River in old times; and they served other gods. 3 Then I took your father Abraham from the other side of the River, led him throughout all the land of Canaan, and multiplied his descendants and gave him Isaac.
The NKJV appears to be clear that Terah was an idolater. It is probably true that of his 3 sons, Abraham, Nahor, and Haran. Odds are that Nahor was an idolater, since his son Laban had household gods that Rachel stole. That's assuming the fruit doesn't fall far from the tree.
Interestingly, the only record of Haran is his son, Lot. While Lot turned a blind eye to some bad stuff, there's no indication that he was an idolater. He wanted to go with Abraham when Abe went out at God's command.
The Josh passage says plural "fathers" were idolaters, and it offers up Terah as a guilty party. One father, however, is not the plural, "fathers." "Your fathers...dwelt...and served other gods."
Those who dwelt beyond the River were definitely: Terah, Abe, & Nahor. They all did.
Those who "served other gods" were definitely Terah and probably Nahor based on Laban's gods.
One can find no evidence in Abe's life that he had any focus other than the Lord. His was devotion only to the Lord, even to the almost sacrifice of Isaac.
Perhaps it was a "by association" issue that was being addressed. As a boy, Abraham was brought up in idolater Terah's household, so one would have expected him to have been indoctrinated in that practice.
As we refer to many as "cultural Christians" because they come from Christian homes in a Christian culture, perhaps we can acknowledge that Abraham was a "cultural idolater" because he came from an idolatrous home in an idolatrous culture. It could have been something he NEVER bought, and that could have been by design of the Lord who eventually calle Abraham out of that culture.
Thank you so much for sharing your insights, dear brother in Christ!