NATIONAL HARBOR, Md. – Many people find it challenging trying to get along with one or two brothers or sisters.

Imagine trying to cope with 18 siblings.

But the eldest Duggar daughters believe they have found the key to domestic success: humility.

Jinger Duggar told WND that the secret her parents taught their children about how to get along with each other is “to humble yourself.”

And, most importantly, “Admit when you’re wrong.”

She said that is the key to healing relationships when they go wrong.

Jinger said the Duggar parents have set a good example in their relationship with each other, which has taught the children how to respond to one another.

WND’s Gina Loudon recently had the opportunity to speak with the four eldest Duggar daughters, Jinger, Jill, Jessica and Jana.

Their lives have been chronicled in the hit TLC reality series about the Duggar family, “19 Kids & Counting.” The show features parents Jim Bob and Michelle Duggar and their 19 children, nine girls and 10 boys, all of whose names begin with the letter “J.” The series launched in 2008, and season eight begins April 1.

The four sisters, attired modestly but charmingly in floor-length skirts, were at CPAC, the annual gathering of conservatives just outside of Washington, D.C., to tell the world about their new book, “Growing Up Duggar.”

Jill described how the book is primarily addressed to young ladies and is meant to help guide them in their many relationships, with their parents, siblings and, of course, boys.

The key, she told Loudon, is using one’s relationship with God to guide all other relationships.

Jessica is in a relationship right now, one the girls described as a courtship. More than just an opportunity to have fun, the girls called courtship “dating with a purpose.” The purpose is to find out whether the person one is courting is a suitable marriage prospect.

Jana provided an example of the humility they say is the key to their happy home.

“I hope this book will really be an encouragement to young ladies, to know that through the difficult times, through good and bad, that God is always there for them,” she said.

“And we understand,” she added, “we’re normal girls and have the same struggles and the same challenges, just like anyone else. But, if you turn your heart completely to the Lord, He will definitely help and be there for you.”

Follow Garth Kant on Twitter @DCgarth.

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