using musical instruments at any circumstances like islamic songs, non-islamic songs or any other context, is not permissible.

My question is about business of my elder brother. He imports musical instruments (various types) and supply those to the shops throughout our country. So far I know using musical instruments at any circumstances like islamic songs, non-islamic songs or any other context, is not permissible. 

So, kindly let us whether selling those is permissible or not. He claims that in some cases music instm. is permitted  to use. I don't know what are those. If there are really any such case plz also let me know. In this regard I like to inform you that, through online I could collect some vedio of one of world renowned islamic intellectual (I don't want to say his name). No doubt the vedio helps to get some important knowledge and also increases the strength of Imaan (more or less). But the fact is- the vedios are full of music. Now, I would like to know are this vedio is one of the such occassions where musics are permissible (that my brother claims)? I'll be really grateful for your ans.