Props Martin Dreyer and Njabulo Gumede, hooker Alandre van Rooyen and lock forward Freddy Ngoza will join the Southern Kings with immediate effect.
All will move for the duration of the tournament, although the BBC could call Gumede back if needed.
Current Blue Bulls players Dayan van der Westhuizen and Irne Herbst were among those loaned to the Southern Kings during the Super Rugby tournament.
BBC High Performance Manager, Xander Janse van Rensburg, said: "This decision will not only benefit the Kings, but SA Rugby as well and will of course give our players good exposure in a different environment and competition. We contracted all of them in the first place because we value their abilities, but can also not ignore the needs of the players and the bigger picture in SA Rugby. The BBC would like to wish all the guys well in the PRO14 and believe all of them will make a considerable impact for the Southern Kings."
Dreyer has played Super Rugby for the Bulls and Stormers, while Gumede is a former Junior Springboks prop. Van Rooyen and Ngoza played for the Blue Bulls in the SuperSport Rugby Challenge.
Janse van Rensburg also confirmed that Jacobie Adriaanse has been released to join the Golden Lions for the remainder of the season.
Southern Kings' PRO14 squad (more players expected to be added):Berton Klaasen, Bobby de Wee, CJ Velleman, Cornal Hendricks, Dries van Schalkwyk, Jacques Nel, Jarryd Sage, Khaya Majola, Lubabalo Mtyanda, Lusanda Badiyana, Masixole Banda, Ntabeni Dukisa, Oliver Zono, Pieter-Steyn de Wet, Rowan Gouws, S’bura Sithole, Schalk Ferreira, Stephan Greeff, Stephan Coetzee, Tango Balekile, Tienie Burger, Victor Sekekete, Yaw Penxe, Kurt Coleman, Martin Dreyer, Njabulo Gumede, Alandre van Rooyen, Freddy Ngoza