Kate and Anna McGarrigle "with family and friends" perform at the Mariposa Festival in Barrie, Ontario, June 23rd, 1989.
Performing with Kate and Anna are their sister Jane McGarrigle, Anna's husband Dane Lanken, Kate's children Rufus Wainwright (16) and Martha Wainwright (13), Anna's and Dane's children Sylvan Lanken (11) and Lily Lanken (10), Joel Zifkin, Chaim Tannenbaum, and Danny Greenspoon.
The source for this clip is of poor quality (VHS EP, linear audio) but it's great to have nevertheless. A friend caught this by chance when flipping channels one day many years ago, threw a tape into the VCR, and recorded it for me.
It's only a fragment but it's a delight. All Stephen Foster songs. First is the ending of "Ah! May the Red Rose Live Alway" featuring Rufus on trumpet and Martha singing lead vocal. This is followed by a version of "Hard Times Come Again No More" in which the kids sing most of the vocals (Rufus singing lead). Then "Gentle Annie" with Kate on piano and Kate and Anna singing. Finally Dane leads a version of "Oh Susannah" with everyone else singing along on the choruses.