The sisters have thanked their 'special twin power' for the successful birth after medical officials unable to help.
Originally, the twins were supposed to have their babies 13 days apart, but fate had other plans.
While the Massachusetts twins live two hours away from each other, they ended up giving birth together at Mount Auburn Hospital.
In ann post on Facebook, Rachael wrote: 'Twin Power: After 2.5 days of trying to induce me and nothing working, we knew we needed to be together.
'Bec came up to Boston to hold my hand and I finally went into active labour. As she and Bill were supporting me, she went into labour too.'
Their husbands, Rachael's Bill Bubenicek and Beck's William Pistone stood by their wives side to welcome their bundles of joy.
'Bec and crew were banging on the walls as they heard our baby William born at 10:41pm!' Rachael posted.
William Charles Bubenick was born first on August 15, while his cousin Andi Isabella came into the world 20 hours later after some twin sister help.
Rachael said: 'The nurses/midwives helped me sneak in with baby William so she could meet and hold him.'
'We sat with her and shortly after she was fully dilated and pushed Andi out in 24 miss! So they are only 20 hours apart!'
'Big thanks to Bec and Todd for forfeiting their plans to have Andi at Cape Cod Hospital.'
This article originally appeared on New Idea.