It's a family affair in the Olympic arenas of Athens.

This month, six pairs of American siblings are squaring off for the most public rivalry of their lives — with world-class standing and family bragging rights on the line.

The U.S. team has multiple pairs of brothers and sisters going for the gold in the same sport — including two sets of twins: In tennis, Mike and Bob Bryan; and in gymnastics, Morgan and Paul Hamm. In diving, brothers Justin and Troy Dumais will both compete. On the fencing team, two sets of sibs — Emily and Sada Jacobson and Keeth and Erin Smart — will duel. And Tara and Dana Kirk are the first sisters to make a U.S. Olympic swim team.

Competing against the most elite athletes in the world is hard enough, but challenging the one you grew up with creates unique circumstances, both good and bad, according to Dr. Ronald Kamm (search), a sport psychiatrist in Oakhurst, N.J.

With the 2004 games surrounded by the threat of terror, having a family around is like a security blanket, said Kamm.

"Your security, literally, is threatened," he said. "Any time you can be with a sibling, even if you don’t get along that well, it's family and you feel better."

Jeff Bukantz (search), the non-competing captain of the U.S. fencing team, expects the siblings on his team to be supportive of each other — but said it's not all hugs and kisses between family members with an eye on the top prize.

"Lets face it, they are going to be competing for an Olympic medal," said Bukantz. "It's always going to be a huge sibling rivalry."

Yale student Sada Jacobson (search), 21, is the first U.S. woman ranked No. 1 in the world in saber. In Athens she may square off with her sister Emily, 19, who qualified in the same event, if they draw each other in the round of eight.

Bukantz said in this case, the sisterly bond will definitely be a benefit.

"I think it will be very good for Emily to have Sada there, they are always together. This is the big one, this is the first time women's saber will be in the Olympics."

Bukantz added that having a sibling competing in a sport is particularly helpful when one has more experience than the other, as is the case with brother and sister fencers Keeth and Erin Smart (search).

"Keeth is the only returning Olympian on our team, and can let [Erin] know the ropes, let her know pitfalls first-time Olympians might run into."

Being close to a sibling is helpful behind the scenes, but Kamm said focusing on the other family member can be detrimental.

"You have to keep the focus on yourself and feel comfortable with any competitive feelings you do have," Kamm said. "Sibling rivalry exists and we do want to best our siblings. Older ones don't want younger surpassing them and younger ones always dreamed of beating the older."

Indeed, Kamm said the competition goes much deeper than the glory of the game.

"Wanting bragging rights within the family is natural," said Kamm. "That's where it all begins. If you are number one in the family, psychologically that can be more important than being number one in the world."

When it comes to this Olympics (search), Bukantz said he's sure the sibling teammates will look at each other the same as any other opponent.

"They have wills of steel and don't see their sister when they go out there. They just see another competitor who they want to steamroll."

And while the Olympics is the pinnacle of sport, Kamm said for family the competition is always high.

"I would agree that the Olympics are the ultimate, it's ratcheted up a notch, but believe me it's pretty high at the local tennis court too."