The Youtube channel Webportalavro which is the Dutch TV company that broadcasted the music show TopPop, have posted a bonanza of clips from back in the day. Sister Sledge have a whole bunch.
The first four are from the sisters CHIC produced output. Then two from their direct follow-up, the very CHIC-ish "All American Girls" album produced by Narada Michael Walden in 1981.
Webportalavro on Youtube GO!
Sister Sledge "We Are Family" (1979) album info GO!
Sister Sledge "Love Somebody Today" (1980) album info GO!