So are you recommending that children being sent to public school refuse to attend school?
Being employed is not the same thing as taking part to join in prayer or listening to a sermon by a heretic.
What if you are employed but don't take part in prayer? Are you saying that it is a sin, in of itself, for a Catholic to be employed at a Protestant church as a musician?
Being present at a Protestant (or Buddhist, or ____) service does not automatically mean that you actively participate in their heresy. For all all I know, a Catholic employed as an organist for a Protestant church could be praying the Rosary silently during the "pastor's" sermon instead of attentively listening.
I don't mean to be condescending. But the main issue of this thread is one close to my heart.
Not taking part requires you to do Nothing! Literally standing there protesting the service. It is licit to attend on say a wedding or funeral of a family member but to attempt to use it as a Sunday obligation being fullfilled as you suggested to the lad is rediculous. You cannot play an organ at a novus ordo or protestant service. If you do ANYTHING that makes ANYONE believe that their service is legitamate then you are in the sin of scandal.
I suggest you read the links I put up BEFORE you made your post since they are articles made by SSPX Priests that say to not attend the Novus Ordo.
I can find something on sending ones kids to Public schools too if you want, since it is the position of the SSPX that Society Schools or Home Schools are the best forms of education for your children. Baring necessity of course.
I don't believe working for a Protestant Church could be licit, it's like someone trying to justify working for an abortionist saying "but I don't kill the babies"
Mortal Sin is Mortal Sin, Scandal(Making someone believe that doing something wrong is ok) is Scandal.
I would advise him to not attend the Novus Ordo. If he lived within a couple hours of me, I might even pick him up take him to his nearest Tridentine Mass and try and arrange someone there to pick him up every Sunday.