Salam Br. Tayo. If I correctly understood your post, you are basing your conclusions on the Arabic word “ābāihim” in 6:87. Your conclusions are not tenable when I analyze this word. This word is derived from hamza bā wāw, and is used to mean all of the following: Fathers, Forefathers, Uncles, Parents, Grand and Grand---grand parents, etc. It is also used both literally, proverbially, biological, and non-biological such as adopted relations. In Quran, the variants of this word are mostly used in collective plural sense of forefathers/uncles/granfathers, etc. One can narrow down the range of meanings based on the context etc. Thus, the correct meanings of 6:87 could be rendered as:
[6:87]: And [some] among their fathers/forefathers/grandfathers/uncles and their descendants and their brothers - and We chose them and We guided them to a straight path.
As an example, let us leave the father aspect aside, 6:87 says “their brothers” as well. Would this mean biological brothers even if some may not have their brothers? Of course the brothers here do not mean only and only biological relations, same way fathers/forefathers does not mean immediate biological fathers. Similarly, God says in [9:23]: “ O you who have believed, do not take your fathers/grandfathers/uncles or your BROTHERS as allies if they have preferred disbelief over belief. …” Does this mean ALL BELIEVERS have BROTHERS? Of course not, it is to be taken in general collective sense. Thus, in my view, verse 6:87 does not support your blanket conclusion.