The pair were loaned to National First Division teams last season, with Hlongwa notably captaining Real Kings to fourth spot in the second tier, while Mthethwa helped Richards Bay FC narrowly survive relegation.
Bucs official Floyd Mbele confirmed both defenders will report for pre-season training.
"This also happens to all our players that were loaned out last season," Mbele says.
"The coaches will have time to look at them."
Mbele also confirmed that Zimbabwean playmaker Kudakwashe Mahachi will land back in the country next week to start his tenure with the Buccaneers.
The former Golden Arrows man is one of nine new signings made by the Soweto giants, who will compete in the CAF Champions League again following their runners-up finish in the Absa Premiership in 2017/18.