ABC News' Hamish Macdonald and Christine Rakowsky report:
Renee and John Thomas of Minnetrista, Minn., adopted Jack from the Kursk region of Russia in 2008 when he was just 4.
"My dream of being a mom happened," Renee Thomas said. "It was all those emotions that I would say you'd go through as if you were having your own baby."
For five years, the Thomases lived as a happy, healthy family but feeling "incomplete," they said. That's because as they adopted Jack, now 8, the couple found out that he had a younger brother named Nikolai still living in a Russian orphanage.
"I really want to see him," Jack said. "And if he came home tonight, we'd have a big party and we'd have chocolate and watch movies and have popcorn."
Almost four years ago, the Thomases were close to reuniting the brothers. They first visited Nikolai in December 2009 with plans to pick him up in April 2010.
"It was a certainty," Renee Thomas said. "I thought absolutely it was going to be like my first adoption-that we'd leave and go home, and we'd be back to pick him up. There was never a thought in my mind that we wouldn't return to bring him home."
After a few high-profile cases in which Russian children adopted by Americans were found abused or dead, Russia decided in 2012 to issue a ban on US-Russian adoptions.
"It means everything to us to be able to have his brother home and raise them together," Renee Thomas said. "We wouldn't be fighting so hard if it didn't mean so much to us."
Renee Thomas has a tough audience though. Russians have been outraged over recent stories in the media.
Artyem Saviliev was 7 when he was adopted in 2010 by a Tennessee woman who sent him back to Russia alone on a plane with a note saying that he was no longer wanted. And toddler Dima Yakovlev died in 2008 when his new father left him in a hot car in a Washington, D.C., suburb. The father was found not guilty of involuntary manslaughter.
"There are no chances for these families to adopt Russian child," said Anton Zharov, a Russian adoption lawyer. "No chance."
Jack's brother is now one of hundreds of pending adoption cases affected by the ban. All of the children currently reside in Russian orphanages.
With well-documented tensions between Moscow and Washington, politicians and lawyers in Russia told ABC News that this was, in part, a political move made by Russia, with young children in the middle.
"[Nikolai's] right to be with his brother should not be subject to any law, U.S. or abroad," John Thomas said.