Seriously. They shared a house and shared hotel rooms. Rumor has it that they even admitted to occasionally sharing a toothbrush.
Early on, the two had visions of their future. They repeatedly talked about when they would get married and buy a bigger house, where their two families would live together.
They believed one day that would happen, but as they eventually discovered, matters of the heart tend not to conform to the best laid plans. So these days, they continue to share a doubles career that has made them the most successful team in tennis history, and also share fronting The Bryan Brothers Band. But as far as their personal lives, they've moved in separate directions. And during the offseason last year they even trained separately for the first time.
Bob fell in love with Miami's Michelle Alvarez and Mike found his match in London's Lucille Williams. Bob and Michelle married in December 2010, reside in Sunny Isles, Fla. (just north of Miami), and welcomed their daughter, Micaela, on Jan. 31 of this year. Mike was engaged to Lucille late last year and will wed in Santa Barbara, Calif., in November. Mike and Lucille live in the house where both brothers resided in their hometown of Camarillo, Calif. Mike bought out Bob's half of the property.
Mike understands that Bob's life has moved at a little faster pace than his own, and he's comfortable with it.
"His priorities have shifted and I come third in his life now," said Mike, after the two won their first-round match at the Delray Beach Tennis Championships on Wednesday. "Like he's going down to be with his family tonight. It's cool. I'm loving experiencing [it]; I'm part of his life, and I'm doing the uncle thing pretty often."
It's hard to erase a bond that started in the womb, however, so it was no surprise that Mike immediately flew to Miami the day after his niece was born. Bob is making sure to include his twin in the baby experience. The doting daddy already has snapped about 2,000 photos of Micaela -- he's counting -- and has sent every picture to Mike. Playing the proud uncle, Mike quickly held up his cell phone and rolled through all the Micaela photos.
An equal opportunity guy, Bob is also acquainting Mike with some of the less thrilling aspects of fatherhood -- a glimpse to the future, perhaps. Diaper changing, anyone?
"Mike and I did one yesterday," said Bob, laughing through the story. "I was like, 'Mike, she needs a diaper change so come and help me, man, you've got to see it.' It was an adventure. It was like, 'uh-oh,' and it was like a scene out of a movie. We changed the diaper three times during the change. There was poop flying everywhere, poop and pee."
"Oh man, it was my first diaper," added Mike, shaking his head and smiling. "It was real."
Bob learned quickly that being a famous tennis player doesn't absolve you from fatherly diaper duty. It also doesn't prevent you from being sleep-deprived.
"I was dragging in the practice sessions earlier this week, and I was testy," Bob said. "I was low on the zzzz's. Last night I did [get sleep]. I came up here and checked into the hotel and I slept for 11-and-a-half hours, and when the alarm woke me up I was in a coma."
David MacPherson, a former player and the Bryans' longtime coach, believes the two have the baby business under control.
"They both are naturals," said MacPherson, a father of two. "I think Bob is loving every minute of it. He hasn't asked for any tips, but it's been about 11 years since I've changed a diaper, so I'm not sure I'd be very helpful."
At Delray Beach, the Bryans were back on the court together for the first time since the Australian Open. Although Bob has been busy being a dad, Mike did go to Switzerland, where he played with Mardy Fish to help the U.S. to a surprising 5-0 win in Davis Cup first-round competition.
Bob and Mike have won 75 titles together, which makes them the winningest doubles team in history, and they hold 11 Grand Slam titles, more than any other active team. Thus far, they've ended seven seasons, including 2011, as the No. 1 team in the rankings.
The Bryans have an impressive 10-1 record in matches this season, with one title at Sydney. They arrived in Melbourne as the reigning three-time Australian Open champions and had won five of the past six titles there. But this year, Bob was far away from home and hoping to make it back in time for Micaela's birth -- his wife's due date was Sunday, Jan. 30. He spent much of his time when he wasn't on the court on his iPad doing FaceTime with his wife, who was half a continent away. Bob and Mike ended up losing in the final in Melbourne to Leander Paes and Radek Stepanek.
"It was a tough one to lose," said Bob, who made it home in time to see his daughter born. "Once that match finished, I really turned into baby mode and I was looking forward to my little girl. It definitely made the loss sting a little bit less. My mind was already back home the minute I walked off the court, and looking back on it, it was a good effort to stay focused with so much stuff going on."
The Bryans are about to turn 34 at the end of April, and like many guys their age, they have family on their minds. Retirement, however, is not even receiving brief consideration. They plan to play -- they hope -- for at least another five years.
"All the doubles players are getting older and older," Bob said. "If you look at the rankings now, we're 33 and we're some of the youngest guys up there. This is a good lifestyle. Everyone who retires tells us, 'Geez, you've got a good gig, so keep doing it.'"
Sandra Harwitt is a freelance tennis writer for ESPN.com.