Wedding Unity Candle Ceremony How Can We Make The Unity Candle Ceremony Work At My Sister's Wedding??

How can we make the Unity Candle Ceremony work at my sister's wedding?? - wedding unity candle ceremony

My sister is still married in October and she and her boyfriend planned to use the unity candle ceremony. (two candles by the mothers for the lighting of a candle for the bride and groom separately) Our mother died several years ago and the wife of my father as soon as the fact that there are married children. Who do you think would be appropriate to light a candle instead of my mother?