I think it is what the scriptures teach. Another point that could be made how narrowly Jehovah’s Witnesses define the word brother in that parable that you quoted. I disassociated from the Watchtower in mid 2006 yet before that I was a died in the wool JW for nearly 30 years (baptized in 1977, February). As far as I know they have not released any “new light” from the “wide awake John class) on the subject, but up until that time at least “brother” was very narrowly defined. It is defined to mean only those that are in the new covenant with Jesus to be his “bride”.
In the Jewish scheme of things, that is not the case and the ones listening to Jesus would not have taken the very narrow meaning of that word. In Jewish culture your brother was anyone who could trace their line of lineage to the existing Patriarch or head of the “family”
A good illustration of this is the patriarch’s Abraham, Isaac and Jacob, from oldest to youngest. Although Abraham is grandfather to Jacob, Jacob would consider Abraham his “Father” and would refer to him as Father Abraham since Abraham was the patriarch in that system. The same would be true for Jacob’s sons and grandson’s if they were alive simultaneously with Abraham. But, anyone else in your family tree, especially the males, if you were not referring to them by name, you would consider your “brother”. This is the brother that Jesus is talking about and the family tree that he is using this term with is a spiritual family tree, not of genetic lineage.
So, instead Jesus is referring to salvation covenant lineage and their respective families and “brothers”. Since Abraham is the mediator of two covenants with Jehovah God, he becomes the “father” of all those who express a faith like his whether they are circumcised or not. Abraham is the “Father” of all those with faith, those who express real faith but have not been compelled to join a true faith (circumcision) and he is the Father of those that have real faith and then are “circumcised”, which for the Jews would have been actual circumcision, but for those in the Christian era would be baptism.
So, all men and women with true faith in God can be said to be Abraham’s covenant children and their relationship with each other is that they are brothers. Isaac is the first one to be circumcised, therefore he is the Father of all those who have faith and then follow that up by joining the true church of their age (if it was there). Isaac is the Father of all those such defined and they are brothers with the rest of Isaac’s children and Abraham’s since Father Isaac is son to Father Abraham. Jacob, Abraham was told would be Father of a great number of children who were represented by the Stars of Heaven. These are those that have faith in God, were motivated to get (circumcised or baptized) into the true faith of the time, and were selected by God to be his son or daughter, being “born again”. Those “born again” would view Jacob as their covenant Father. Jacob’s son’s would be all those in his family tree. These ones would view any still alive from the families of Abraham, and Isaac to be their “brothers”
It is the same today, even though we are not Jewish (at least most of us, I think). But everyone with “faith” (without circumcision or baptism) is our spiritual brother if we too have faith. All those who have faith and join a true faith of their time are also our brother. And lastly, all those who have faith, have been baptized into the true faith of the time are also our “brother’s” including “those born again, and the remnant of the Bride of Christ.
This is how I think we are to take the parable of the sheep and the goats. During the time of trouble that is going to happen soon in this system of things, dreadful times will be here for a short time. Our brothers, many of whom we do not even know are our “brothers” will find themselves in dire need of a meal, some warmth, or any number of perilous situations. What will we do at that time, even if our “faith” seems to be waning? Hopefully, for our sakes, we will be motivated by the love that Jesus spoke about in this parable. Even at the cost of our own lives, will we show love for our “brother”, Jesus “brother”? You see, even though Jesus was and is the “Son of God”, he was also in the family tree of all the patriarch’s of his day. So, all the ones that we described earlier are Jesus “brothers”, not just those who are engaged with him to be married as is taught by the sleepy John class in the Watchtower.
If you have faith, but nothing more Abraham is your covenant Father through his mediator-ship of that faith covenant. If you have faith and were motivated to get baptized into the true faith of this time, your covenant Father is Isaac, and if you are a person with faith, who was baptized, and later received the token of your being adopted by Jehovah as his son or daughter, your covenant Father is Jacob, and if later brought into the new covenant with Jesus to be his bride, Jesus is your covenant Father. But, the entire spiritual family tree are Jesus “brothers” so we should look out for every opportunity to show real love for them.
True love is what Jehovah and Jesus are attempting to cultivate in us as their children. It is not easy to achieve in this system and will be even harder when we come under the love test. Keep the words of Jesus in mind as these days quickly approach and resolve in your heart that when the time comes, you will show ‘the tested quality of faith” and love at that time. If you do, Jesus will be proud to call you his “brother”. I think this is true even of those who now lack faith. If they show this kind of Love when tested to the max, Jehovah and Jesus are willing to take a chance on them in the 1,000 year Kingdom of God.