Nominal: being such in name only; so-called; putative: not in reality.
False Christians don't have a heart to lead someone to Christ or confess the Lord before others (Matt. 10.32-33). Only if asked by a Christian will they respond they believe because they know that's what the Christian wants to hear. They did not mention Christ all these years you knew them, nor did they rejoice when you yourself got saved. They have no passion for Christ. It is as though Jesus is dead and stayed dead to them.
They have never tried to lead those close to them who are not Christians, not even their own children or parents or brothers and sisters. They don't read the Bible. Their only friends are non-Christians. After you got saved and tried to lead them to Christ they remained hostile, but over time did an about face. They changed their story and introduced the idea of their confirmation as a child just because one time they remembered going to Church as a child. Now they can claim they got saved before you. How vain and pretentious! They don't go to Church. They have no fellowship with the body of Christ. Even when talking to them still all their opinions are so contrary to the spirit of Scripture. How utterly painful for them to hear anything about the Scriptures!
Along the way they may mention belief in reincarnation or that one should not mention Hell or that most people are saved anyway. It is Gods decision they say. Is that how you read the Bible? Why does Jesus talk about Hell so much and the clear way of salvation if that is the case? They shut their minds down, busying themselves in the world. There is no budging them. If they really were Christians, the Church would not exist for their participation is non-existent and would be a silent church.
Deu 6:4 The LORD our God [is] one LORD: Deu 6:5 And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might. Deu 6:6 And these words, which I command thee this day, shall be in thine heart: Deu 6:7 And thou shalt teach them diligently unto thy children, and shalt talk of them when thou sittest in thine house, and when thou walkest by the way, and when thou liest down, and when thou risest up. Deu 6:8 And thou shalt bind them for a sign upon thine hand, and they shall be as frontlets between thine eyes. Deu 6:9 And thou shalt write them upon the posts of thy house, and on thy gates.
If you are ashamed of Jesus, He will be ashamed of you. "Whosoever therefore shall be ashamed of me and of my words in this adulterous and sinful generation; of him also shall the Son of man be ashamed, when he cometh in the glory of his Father with the holy angels" (Mark 8.38).
I even ask them, what is the Trinity? And they don't know.