The inexperienced pair will join Silver Ferns shooter Daneka Wipiiti and Paula Griffin, who has moved south from the Wellington-based Central Pulse in a bid to reclaim her spot in the national team.
The most notable omission from the team which reached the playoffs this season is the captain Megan Dehn.
The franchise had hoped the goal attack would qualify to play for the Steel as a New Zealand resident, but the former Australian international ran into difficulties obtaining citizenship.
According to The New Zealand Herald, Dehn is set to be named in the Northern Mystics squad when the teams are released today.
The Mystics have taken advantage of Dehn's citizenship difficulties and were able to secure the veteran.
Dehn said after failing to secure her residency she was considering retiring, but Mystics captain Temepara George convinced her to make the move to Auckland for one last hurrah.
With the Steel's overseas slot filled with Australian midcourter Natasha Chokljat, and back-up shooter Julianna Naoupu lured away by the Waikato-Bay of Plenty Magic, the combined Otago-Southland team will have to rely heavily on Wipiiti and Griffin to carry the scoring responsibilities.
While Selby-Rickit and Fenwick are rated highly, the young pair are light on experience.
Selby-Rickit is just 18 and 17-year-old Fenwick is still at school.
The ANZ Championship is not the place for development, but if injury strikes, the Steel will be forced to call on one of its teenagers.
That is a worry for coach Robyn Broughton, who told the Otago Daily Times earlier in the week she believed the franchise made a mistake signing Chokljat before it had secured Dehn's services for next year.
However, the addition of Chokljat does give the Steel midcourt a more solid look.
The Invercargill-based team was well-served at both ends but struggled in the centre, where it lacked the dynamism of some of the other teams.
Steel chief executive Julie Paterson said the decision to recruit Chokljat was made in consultation with Dehn, who initially indicated she was considering retiring.
"When Megan later confirmed she was keen to play another season, we were obviously keen to have her," Paterson said.
"While the outcome is obviously not the one we desired, we have to move on and we are looking forward to the exciting challenges ahead in 2011."
Selby-Rickit could not be reached for comment but Fenwick, a year 13 student at Rangi Ruru Girls' School in Christchurch, said she was very excited to secure a Steel contract.
"It's a great opportunity and I'm really looking forward to it," she said.
"There are some really great names in there. It will be awesome to play alongside them."
Fenwick has been part of the Canterbury national championship side for the past two years and has also played for the New Zealand Secondary School team.
Selby-Rickit is no stranger to the Steel.
She was called into the squad this year when Wipiiti was unavailable due to injury.
Her older sister Te Huinga Reo Selby-Rickit has been a member of the squad for the past three years and, with Silver Fern goal keep Leana de Bruin, leads an impressive defensive line-up which includes former international Sheryl Scanlan.
Silver Fern Liana Barrett-Chase and Wendy Frew return to round out a talented midcourt which includes Otago player Hayley Saunders.
Liana Barrett-Chase, Erika Burgess, Natasha Chokljat, Leana de Bruin, Sophia Fenwick, Wendy Frew, Paula Griffin, Hayley Saunders, Sheryl Scanlan, Te Huinga Reo Selby-Rickit, Te Paea Selby-Rickit, Daneka Wipiiti.