Is this Blasphemy

well, my problem is this, my father is an atheist but used to be Catholic, and when he was a kid they sang a song in the Church that he did never understood, so he sang nonsenses, now he sometimes sing it like that.

but the problem is my brother sometimes sings it like that also, because he finds it funny because it actually sounds like what my father sings (which like i told you are just nonsenses, some of the parts are not even words).

so my question is, is it somekind of blasphemy to change the lyrics of the music in the Church, when you are not trying to offend God with it.

I would worry more that he is a fallen away Catholic than what he sings. That is going to be more problematic for him.
Once you are Catholic, there is no “used to be” Catholic. That is a misconception people have.
Try to discern WHY he stopped practicing his faith. WHY he identifies as an atheist, and if he is closed off to talking about it, so that maybe you can help him to return to the Church.
That is far more important at this time.
Pray for the words to say, to have a open dialog with him about this. As the Holy Spirit to guide you. He’s your dad. It’s really important.
God bless.

No…

Modern Catholic Dictionary:

BLASPHEMY. Speaking against God in a contemptuous, scornful, or abusive manner. Included under blasphemy are offenses committed by thought, word, or action. Serious contemptuous ridicule of the saints, sacred objects, or of persons consecrated to God is also blasphemous because God is indirectly attacked. Blasphemy is a grave violation of charity toward God. Its gravity may be judged by the capital punishment in the Old Testament, severe penalties of the Church, and in many cases also of the State for blasphemous speech or conduct. In order for a person to sin gravely in this manner, he must use blasphemous expressions and realize the contemptuous meaning of what he says or does. (Etym. Latin blasphemia, blasphemy; from Greek blasphēmein, to speak ill of.)

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