I am uncertain what you mean by “the least of Messiah’s brethren.” The Jews were Christ’s ethnic brethren and I believe many Jews will yet come to understand He is the only way to eternal life. Outside of Christ, there’s no eternal hope for any man, Jew or Gentile.
“Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me.”
“And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.”
I have no idea if Josh Duggar has ever been born again, but if he has, his sin has been forgiven because Christ paid the sin debt in full for His church at Calvary. If Josh Duggar has been born again he has been given a new heart and a new nature, but he still has his old nature and right now he’s a conflicted soul.
Here’s how Paul described that conflict within himself:
“18 For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. 19 For I do not do the good I want, but the evil I do not want is what I keep on doing. 20 Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me.”
—Romans 7:18-20
Walking an aisle and having a conversion experience never saved anyone. Just as a dead man can’t decide to live, a man dead in trespasses and sins cannot decide to be spiritually reborn into God’s kingdom. Being regenerated (or born again) is a miracle of grace performed by the Holy Spirit in the heart of an undeserving hell-bound sinner. When Nicodemus asked how he could be born again, Jesus didn’t tell him to pray, walk an aisle, make a decision, or do anything whatsoever. In fact, he said that which is born of the flesh is flesh. Flesh always begets flesh. Instead of telling him to do something, Jesus said something that clearly perplexed Nicodemus. He likened the work of the Spirit to the wind.
“Do not marvel that I said to you, ‘You must be born again.’ The wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.”
—John 3:7-8
“For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.”
—Ephesians 2:8-9
This is what I mean (bold emphasis mine). When the Son of man shall come in his glory, and all the holy angels with him, then shall he sit upon the throne of his glory: And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats: And he shall set the sheep on his right hand, but the goats on the left. Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world: For I was an hungred, and ye gave me meat: I was thirsty, and ye gave me drink: I was a stranger, and ye took me in: Naked, and ye clothed me: I was sick, and ye visited me: I was in prison, and ye came unto me. Then shall the righteous answer him, saying, Lord, when saw we thee an hungred, and fed thee? or thirsty, and gave thee drink? When saw we thee a stranger, and took thee in? or naked, and clothed thee? Or when saw we thee sick, or in prison, and came unto thee? And the King shall answer and say unto them, Verily I say unto you, Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me. Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels: For I was an hungred, and ye gave me no meat: I was thirsty, and ye gave me no drink: I was a stranger, and ye took me not in: naked, and ye clothed me not: sick, and in prison, and ye visited me not. Then shall they also answer him, saying, Lord, when saw we thee an hungred, or athirst, or a stranger, or naked, or sick, or in prison, and did not minister unto thee? Then shall he answer them, saying, Verily I say unto you, Inasmuch as ye did it not to one of the least of these, ye did it not to me. And these shall go away into everlasting punishment: but the righteous into life eternal.
Matthew, Catholic chapter twenty five, Protestant verses thirty one to forty six,
as authorized, but not authored, by King James
I have no idea if Josh Duggar has ever been born again,
Then I submit you should also have no idea if Luther has ever been born again either.