Family On Edge As American Couple Still Unaccounted For in Belgium

An American husband and wife are still missing in Belgium following Tuesday's attacks and their families are on edge as they try and fail to contact the couple.

Stephanie and Justin Shults moved to Belgium in 2014 and were at the tail end of a visit from Stephanie's mom when a tearful goodbye at the airport took a tragic turn.

Suicide bombers set off their deadly devices just as Stephanie's mother, Carolyn, made her way to security.

"Carolyn was on her way home," Larry Newson, husband to Carolyn's sister Betty, told InsideEdition.com. "They waved goodbye and then the bomb went off."

Read: Three American Mormon Missionaries, U.S. Military Family Among Injured in Brussels

The couple have lived and worked in Belgium since moving there in 2014. Stephanie is originally from Kentucky. Justin is from Tennessee.

While Stephanie's mother is now safe at a Brussels hotel, her daughter and son-in-law remain missing and their phones are both going straight to voicemail.

"They're not on any of the [victims] lists," Mr. Newsom said, which has forced authorities to go from hospital to hospital in search of the couple.

According to Newsom, another member of the family intends to head to Belgium to help Carolyn as the search for Stephanie and Justin continues.

Read: Mom of Twins Who Was Flying to New York is First Confirmed Victim of Brussels Attacks

Meanwhile, two New York siblings are also missing after the airport blast, which killed 11 and left around 100 injured.

Alexander Pinczowski and his sister Sascha Pinczowski remain unaccounted for Wednesday. They had recently checked in with a relative on the phone when the bombs went off. No one has spoken to them since.

Alexander Pinczowski's friend Karen Jones Cage is now helping lead an online search for the siblings.

"We are still looking for Alexander Pinczowski and his sister Sascha. They are missing in the Brussels airport attack since this morning," Cage wrote on Facebook as part of a string of anxious messages.

Watch: How You Can Be Prepared if a Terrorist Attack Occurs During Your Commute