Ashley, Hannah, and Will Ashley Schaus and her sister Hannah both accepted their proposals from Will Seaton. (Photo: Ashley Schaus/Facebook)

When Will Seaton, 25, decided to propose to his girlfriend, Ashley Schaus, 23, he knew he'd need more than one ring. That's because in addition to asking Schaus to be his wife, he also wanted to ask her little sister, Hannah, to be his best friend forever.

Will and Ashley's story actually began seven years ago when the couple met during a car show in Bristol, Indiana. Right from the start, Schaus joked with Seaton that she and her sister were a package deal. Sixteen-year-old Hannah has Down syndrome and is diabetic and will always need to be in her older sister's care. In an interview with the "Today" show, Schaus recalled telling Seaton soon after they began dating that Hannah is "part of my life and if you’re going to be with me, she’s going to be with us."

Seaton clearly took his girlfriend seriously. In seven years of dating, they've taken Hannah along on most of their dates — to the movies, to dinner and to arcades. So it made sense to Seaton that when he asked Ashley to be his wife, he would also need to ask Hannah to become part of his family.

Seaton popped the question during the Schaus family's yearly photo shoot. But before he asked Ashley to marry him, he got down on one knee, opened a ring box, and asked Hannah to be his best friend forever. Through tears, Ashley asked Seaton if she was next. "Then he got down on one knee and asked me to be his wife," she recalled.

Will Seaton proposes to sisters Hannah and Ashley Schaus. Will Seaton proposes to sisters Hannah and Ashley Schaus. (Photo: Bret & Brandie Photography)

Hannah will have the title of "Best Sister" for the wedding ceremony, which will take place this October. She and Will will also exchange friendship vows (that include promising to share secrets, go fishing, and take care of one another for life.) The two will also share a special dance at the reception to the Harry Nilsson song, "Best Friend."