Usuthu officially unveiled the two players this week, although Bern signed before the start of the season.
The 22-year-old joined on a free-transfer from ABC Motsepe side Cape Town Spurs as 24-year-old Mhlongo signed for AmaZulu after parting ways with Richards Bay last term.
Both players could featue in the Betway Premiership against Siwelele at the Moses Mabhida Stadium on Saturday.
Zwane said in the Sowetan: "Good acquisitions, top-class players. Obviously, we wanted to have them on board earlier, but unfortunately, it didn't happen the way we would have wanted.
“We are just happy that they are finally here. We know that they will add value because they have qualities, both of them.”
AmaZulu are currently in sixth place on the league standings with 18 points from 11 games.
"If you look at how we started and where we are now, I can say that I am partially happy. There are games where we could have done better, especially in games where we scored first but ended up not winning, we didn’t deserve to lose against Polokwane at home."
"We want to turn things around. We want to win the three remaining games before the Afcon recess," added the head coach.
