Both cases are not permissible. However, try to sing with them without the music and if this is totally not possible, you can be there with them and seek Allah’s forgiveness if you desperately need that job and if there is no other alternative for you.

i live in london, theres not many jobs a woman observing niqab can do, i am currently working in a nursery and the national curriculem requires music to be involved in a child’s learning; is it permissible to sing along children’s songs with musical instruments in them? If not is it okay for me to be in their gathering while music is played? Plz reply asap i start work in 2 days.