MMM-Tots! Your Guide to the Ever-Growing Hanson Family Tree

Their newest addition will join the couple's six older children. The five oldest include son Jordan Ezra, 18 next month, daughter Penelope "Penny" Anne, 15, son River Samuel, 14, son Viggo Moriah, 11, and daughter Wilhelmina "Willa" Jane, 8 next month. The travel-loving family documents their adventures on Natalie's blog natonthewall.com.

The youngest of the Hanson clan, 34, married his longtime love in 2006 after five years of dating.

Zac and Kate welcomed the eldest of their four children, a baby boy named John Ira Shepherd, in 2008. Like many of the Hanson kids, Shepherd goes by his middle name. Next to arrive was daughter Junia Rosa Ruth, now 9, followed by son George Abraham Walker, now 6.

Zac and Kate's youngest child joined the family on Aug. 6, 2016. "We are overjoyed to share the arrival of Mary Lucille Diana Hanson," the dad told PEOPLE of the newborn, who will go by Lucille. "It is such an inspiration to meet her and to imagine all of the adventures we will take together as a family of six."

Isaac, 39, was the last of the musical trio to wed. He married Nicole in a Tulsa, Oklahoma, ceremony in 2006.

Isaac and Nicole are parents to daughter Nina Odette, 6, son James Monroe 12, and son Clarke Everett, 13.