Thanks for the reply Biblicist, he tells me he believed he was truly saved according to what he was taught from the scriptures and according to what he was feeling inside emotionally, but then this evangelist "convinced" him he wasn't, or at least caused him to doubt, so he wanted to make sure, so he once again confessed his sins and called upon Jesus Christ to save him just as the scriptures teach how one becomes a child of God. So he is not saying his confessions were false, he is just saying he believes now what he felt inside was not any Spirit of Christ but rather just common emotions that all people can feel if they want to believe something is real.
But this is what we want and teach. We are commanded to raise our children in the Lord and in the church, and not to suffer the little children to come unto Him. And God gives a promise, "Train up a child in the way he should go: and when he is old, he will not depart from it." (Provb22)
You will have to trust what I tell you for I know my brother and I know my nephew well. He was not coerced into calling upon Jesus Christ, he freely wanted to, and believed Jesus would honor his prayer.
I know from scripture and from my own experience that there is a greater witness within me that confirms my salvation over and above even my own flesh (which always is in attack mode), much less any man outside of me. It is from that inner witness I can say I "KNOW" as it is the abiding Spirit that provides that kind of assurance (1 Thes. 1:4) in spite of myself, men or Satan.
You may "know" your brother and nephew, but you cannot possibly know their heart as only God is privy to that. You can only surmise. It is possible to have your faith overthrown so that you doubt your own salvation. However, doubting your own salvation is one thing, denying there is a God is quite another thing and proclaiming to be an atheist. If such is the product of having their faith overthrown, Paul tells Timothy that God still knows His own even if His own have lost faith in knowing God. Hence, that must be possible.
On the other hand, there are those who were "of us" but who went from us that it might be manifest they were really not of us at all (1 Jn. 2:19). Significantly, the apostle informs us that their departure is the ONLY THING that makes this manifest, not their former profession, not their former life, not their former attitude but only their departure.