Stackhouse announced the additions Tuesday.
Millora-Brown of Lorton, Virginia, started 28 of his 32 games at Rice as a freshman last season, and he led the team shooting 59.8 percent from the floor. He will have to sit out this season and won't be eligible until 2020-21.
A native of Zagreb, Croatia, Jankovic will be eligible this season after spending a year at Monteverde Academy in Florida. Jankovic also played two seasons at Prolific Prep.
The Associated Press contributed to this report.