Mother son dance

My future mother in law just emailed me asking me what song they are dancing too or what the choices are. I told her that we as a couple picked what a wonderful world. She emailed me back that she would like to do a mash up and multiple songs that mean something to them both and gave me the list. Ignoring the fact that I already picked a song with my fiancé. I mentioned this email to him and he said he did not want to do a “mash up” and they do not have songs and they have never even shared any likes or similar interest in music. Nor does he want to dance with her longer then 2 minutes. We have a tight schedule of when we are doing things and we want to keep first dances simple. I’m not sure what I should say or if I should just ignore it. I felt like just ignoring my reply and jumping to what she wanted is disrespectful especially when we said we have chosen it as a couple for them to dance too.