The 17-year-olds, born in Stockholm and capped at Sweden youth level, had been strongly linked with a move to the City Ground in recent weeks before Forest confirmed the deal on their official website. Both have signed academy contracts and will begin life at the club in the under-18 squad.
Academy manager Chris McGuane welcomed the pair, describing them as players the club had monitored for some time before the opportunity to sign them arose.
"We are delighted to welcome both Joseph and Jubilee to Nottingham Forest. Both are players we have followed for a long period, and we are pleased that we were able to tie them to the academy when the opportunity arose," McGuane said.
He added that the twins' attacking instincts were a key part of the appeal.
"Jubilee and Joseph are both offensively-minded players with exciting attributes for creating chances and scoring goals. We look forward to helping them settle in at Nottingham and working with them — both on and off the pitch — as players and as people."
The move continues a growing trend of English clubs recruiting from Reading's academy after the Royals' well-documented off-field turmoil in recent years, with the Ntege twins among several promising young players to leave Berkshire since their release.
Jubilee, a midfielder, scored seven goals for Reading's under-18s in the Premier League U18 competition last season, while Joseph has represented Sweden at youth international level alongside his brother, both having come through the club's academy system together from a young age.
For Forest, the signings represent a low-cost bet on twin talents who arrive with interest from elsewhere in Europe, and whose development the club will now look to accelerate through its academy pathway. The pair becoming teenagers this week — both turn 17 in the coming days — adds a personal milestone to what is already a significant week in their fledgling careers.