The girls, from Pinley Crescent, are running to raise money for a cause close to their hearts - NICHS.
Their “wonderful” dad Paul, who was 59, passed away suddenly on November 23, 2021, while on his way to his work.
Niamh, whose idea it was to take on the challenge, said there’s not a day goes by that she doesn’t think of him.
“In many ways, it still seems like yesterday,” she told the Chronicle.
“I think about him everyday, and it’s hard having to drive past where it all happened when we are leaving the house.
“He’s always on our mind, but it feels like he’s with us.
“If he was still here, he’d be chuffed that we’re doing this for charity - and he’d be torturing everybody for sponsorship!”
The sisters hope that their fundraising for NI Chest, Heart & Stroke will help other families - “so they’ll not be in the same position that we were in”.
“It was my idea to sign up for the half-marathon and I dragged Aisling into it for a bit of moral support,” Niamh, an e-commerce executive, explained.
“Aisling (Down Ladies GAA star) definitely got all the sporty genes in the family, so it’s been more of a challenge for me.
“The training has been going alright. Unfortunately, Aisling can’t always come out with me because of her own commitments to training so, at times, it has been a bit of a slog going out on my own - especially on rainy nights.
“A few months ago I did the Almac Belfast City 10k with a couple of friends. The last few kilometres were tough, but the feeling when you finish is great.
“The event was actually on Father’s Day and, when I found it a struggle, I just kept saying ‘come on dad, help me through this’.
“I think we will both be in the same mindset on the day of the half-marathon.
“I’m really not too bothered about a time, it will just be a matter of getting across the finish line.
“It will be a good day out for the family and I have some friends coming down to cheer us on along the route.”
Their dad Paul was on the committee of Banbridge Town FC and the Crystal Park club has been a huge support to the Cull family.
“After dad passed, the Town held a special day where they raised money for NICHS,” Niamh continued.
“We still have close connections with the club and mum would go down to the home games.”
The girls would love to raise as much money as possible, with their initial target of £500 already exceeded.
“Things are going well so far, and if we got over the £1,500 mark that would be brilliant,” Niamh said.
“Any donations are greatly appreciated.
“It’s a personal challenge to push ourselves, but it’s definitely nice to do something in memory of dad.
“He always said that whatever we were doing in life, he would support us.
“I’m heading to Australia in October and I know he’d be supporting me to go - just like he’d be supporting Aisling out on the football pitch.
“Dad passed away while Aisling was studying for her teaching degree, so it’s sad that he didn’t see her graduate and start her new job in Dundalk.
“It’s hard when he’s not here to share in these special family times.”
Chronicle readers can support Niamh and Aisling’s fundraising for NICHS by donating through JustGiving at: www.justgiving.com/page/niamh-cull-1691851456235
NICHS fight chest, heart and stroke illnesses to improve the lives of people across Northern Ireland.