The twins are the daughters of property developer Bob Carlson (d. October 2001), a devout Christian and Marsha Barbi, a former Miss Ohio, but their parents divorced when the twins were just two. The twins believe that their mother was always a lesbian and when she left their father, she and they traveled to West Hollywood where Marsha became an “outspoken lesbian feminist”. According to the twins, Marsha had numerous lesbian lovers including some quite famous women. Then she met closeted singer Dusty Springfield in 1975 and the two women lived together for two years.

Shane and Sia began modeling at the age of seven when they posed for a layout in the Sears mail-order catalog. As adults, their career has included fashion and mainly pin-up modeling. The Los Angeles Times did a cover story about the Barbi Twins when their billboard went up on Sunset Boulevard in 1989 immediately catapulting them to worldwide attention. In 1989, 1990, and early 1991, they modeled for Chanel, Thierry Mugler, Jean Paul Gaultier, John Galliano and others.

During their recovery, the twins armed themselves with degrees in health and nutrition, and began lecturing in 2000 on “How to eat to live, not live to eat”. They lectured at the Learning Annex, universities and high schools as well as on radio, television and on-line. In early 2001, they came out to the nation on the CBS television program 48HRS in a piece about eating disorders, entitled “Slim Chance.” They also shared their recovery story in a chapter in a celebrity addiction book called Feeding the Fame.

48 Hours did a special on the Barbi Twins in 2002 on their eating disorders, and the E! True Hollywood Story did a biography on the twins in 2001. They also had several guest appearances on talk shows for television and radio, such as The Geraldo Rivera Show and The Howard Stern Show. The twins made several appearances along with William Shatner, John Landis, and many others in the American animated series Eek! The Cat playing twin rocket scientists, “Dr. Shane and Dr. Sia”. In 2007, they received an associate producer credit on Curt Johnson’s animal activist documentary titled Your Mommy Kills Animals, which received highly acclaimed reviews from Variety, The Hollywood Reporter and Los Angeles Times.

In November 2003, the Barbi Twins sued Larry Flynt and Hustler magazine for shots taken at Playboy studios that found their way to Hustler without permission. The twins had a vitamin line they were promoting to be introduced in 2004 and the pictures were never meant to be published. They sued for both the pictures and a fictional story that appeared in Hustler as the Barbi Twins claimed it ruined their health image.

In a 2009 article by Fox News called the twins “the Willie Nelson of pin-up girls interviewing the twins where they spoke of how they (the twins) use their “seven and a half minutes each of fame” to speak out for animals. They participate in animal protests, such as anti-pet shops, anti-puppy mill, anti-circus, and anti-animal experimentation (vivisection) and are vegan. They held a vigil for pets lost during the pet food poisoning that occurred that same year. They also help lobby animal bills, such as the pet food safety bill.

In 2009 they became very active in lobbying in favor of the ROAM act for wild horses along with Willie Nelson, and continued their support speaking openly about the horse slaughter ban, the ban on de-clawing and the fight against factory farms and animal cruelty.

In 2010 the twins again showed their support for the animal community and were featured in the movie Skin Trade, IMDb.

In 2010 they helped bring public awareness to the ban on seal hunting in Canada by doing a media blitz to help end the brutality of seal hunting, the dangers to the sea turtles and other endangered species affected by the BP oil spill, and helped lobby and pass HR5566, the Animal Crush Video Prohibition Act Bill (banning violent images against animals on websites).

In 2011 were featured and voted as one of MAXIM’s Hottest Famous Twins, were featured in numerous movie posters on behalf of animal causes (see Animal Activism below) and on covers and featured articles in True Cowboy Magazine.

The twins participate in animal rescue projects. In 2011, they worked the Animal Welfare Institute to support the ban on horse slaughter. and appeared in the documentary The Petition about the issue.

In 2012 the twins announced their first feature documentary called I HAVE A DREAM about breed discrimination. Breed discrimination was at the root of the recent death of Lennox, a dog that was destroyed just for being a breed too similar to a pit bull. (ExtraTV)

In 2012, the twins spearheaded a movement to track down a person posting online videos of killing kittens, believed to be Luka Magnotta. They have been searching for him since 2008. Their search remained ongoing as of 2014.