"Family" doesn't mean — and has never really meant — a man, a woman, and two kids. Family can refer to single parenthood, cohabitation, same-sex parents, a tight-knit friend group, grandparents or siblings as primary caregivers, or any variation. Mamma Mia! explores several different ideas of family. The most obvious is the mother-daughter duo: Donna and Sophie. Their little family is filled with endless joy, support, and love.
But Rosie and Tanya are also a part of their family. Donna may not get to see them often, but they are very much her sisters. By the end of the film, Sam, Harry, and Bill also agree to be one-third of Sophie's father as Donna is unsure who Sophie's biological father is. This only reinforces the idea that "family" doesn't equate to blood connection.
