Kim Lewullis and Nikki Watts have a lot of things in common. They live on the same block in the same style house in Collegeville, Pa. They both teach at the YMCA. They both have three children.

This makes sense because they were born minutes apart: they're twins. They do one more thing together, too: Run. On Monday, they'll run their second Boston Marathon.

"We try to do all of our long runs together," said Lewullis, 40, who is older by two minutes. "Knowing that we're in this together provides strength and just peace of mind."

"I cannot imagine training without her," said Watts. "She is a huge support to me. I may not even be running marathons if it wasn't for her."

It also helps that all six of their kids can crash at one house with one husband on duty so that they can get in their long runs in, Lewullis joked.

They think they're identical twins, but they're not sure. They've never been tested to confirm their hunch. When they both taught elementary school, sometimes in the same classroom, their students could tell them apart, but those students' parents could not.

Both sisters ran cross-country in high school. Lewullis became a marathoner first through the Marine Corps Marathon 2006. Watts ran her first marathon, the Via Marathon, in 2012. That was Lewullis' second, and they used that time - three hours, 39 minutes, 45 seconds - to qualify for the 2013 Boston Marathon.

The sisters had finished the race and were changing in the bathroom of a hotel when the bombs went off. The hotel went into lockdown, and after finding their husbands, who had been watching at miles 24 and 25, and being allowed out of the hotel, they drove home. "I really don't remember even talking. We did not turn on the radio," said Watts.

The sisters missed qualifying for the 2014 Boston Marathon by one minute, but qualified for 2015 through the Philadelphia Marathon.

It wasn't really a question that they'd be running this year, despite what happened during the 2013 race. "The fans in Boston are overwhelmingly kind to be out standing on street corners to cheer us up. We will not let the evil stop us," Watts said.

For the twins, it will be a weekend celebration of running, and a family affair. "I wanted my oldest, my twins, to go with me this year and experience Boston Marathon Weekend," said Watts.

Both Lewullis and Watts say that they love running with each other - it's a way for them to catch up even though they live on the same block. One drawback to running with your twin though? "That neither of us can slow down," said Lewullis. "When we're running, we are constantly saying 'maybe we should slow down' or 'can you slow down a bit?' but it only lasts for a few seconds."

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