Warrick Gelant and Embrose Papier have extended their contracts with the Bulls until 2020.
Both Boks declined offers from elsewhere, with Western Province reportedly one of the interested parties.
Other players to have extended their contracts with the Bulls include Conraad van Vuuren, Johnny Kotze, Ruan Nortje and Mornay Smith.
Junior Boks prop Alulutho Tshakweni has also signed until the end of the season.
The Bulls also confirmed that utility player Ulrich Beyers has been released to the Kings with immediate effect, while Abongile Nonkontwana is on trial with the Cheetahs.
Photo: Gordon Arons/Gallo Images