Am I obligated to have my fiancés sisters and daughters (so his nieces) in the wedding party as bridesmaids and flower girls??

For the record, no guys from my family are his groomsmen. And I do NOT have a relationship with his sisters (I have met them on two separate occasions in the past year. I dont even have them on social media or talk to them outside of this two times)

The reason for this post is they are mad that I didn't consider them to be in the wedding party and are shitting on my fiancé