McDonald is an attacking midfielder, while fellow 18-year-old Sithole is more defensively-minded in the engine room.
Their elevation was accompanied by the signing from Bidvest Wits of left-back Bokang Thlone, who looks set to miss most of the season with ligament damage.
“The two boys are certainly talented, and disciplined,” Mdluli told the club's website.
“They have showed their willingness to work hard to take the next step forward. I think they will do well, now it’s about how long they will take to adapt to the first team.
“But the kind of coaching they will get in the first team is amazing and I’m sure their speed in becoming professional will happen soon.”
The Team of Choice have also developed the likes of Siphelele Ndlovu, Lebohang Maboe, Fortune Makaringe and Bandile Shandu in recent years. Mdluli says the high-flying Premiership outfit is geared towards bringing through young talent.
“Because of the way we train, everything is on the table and made clear. So for young players with such talent, I’m sure they will adjust quickly and will go far in their careers with the discipline and quality they have.
“I’m grateful that the coach in our Castle [league] side did an excellent job with Lindokuhle and Ujaun. Then they came to the MDC team and did well. So it’s a matter for them now to really make use of their chance with the first team.
“It’s also good for us as coaches working with these young boys to see the first team coaches appreciating our work.
“I’m more than happy. If you check now how many players in our first team are coming from our Diski team and our development U-19 Castle team, we have got a lot. You name them, Shandu, Ndlovu, Maboe, Makaringe, they’ve been there.”