Parents passed away, trying to figure out my brothers mother-son dance

I'm sorry for your losses! I would do something like the sisters sharing a song with your brother. He dances for a minute with the eldest sister, then a minute with middle sister and then a minute with youngest. That will give the photographer a chance to get a good photo of a moment with him and each of you.

This was years and years ago, but I saw this video of a father daughter dance : https://www.youtube.com/watch?v=P6mz7B_uLqc and the bride's brothers put together a special dance and they (and their grandfather) each danced with her for a bit. So split one song, have each person cut in after 45-60 seconds.