Sadiq and Abdullahi both spent last season on loan with Roma's Primavera squad in the Italian youth league, helping Alberto De Rossi's side to win the Italian championship.
Roma have now confirmed they have exercised the option to sign both youngsters permanently, paying €2.5 million for each player.
The 19-year-old Sadiq made his first team debut in November away at Bologna, scoring his first senior goal in a 2-0 win over Genoa in December. The highly rated striker scored twice in six appearances for the senior side last term.
Abduallahi made 18 appearances last term for the Primavera, scoring two goals from his right back position.
The duo was discovered by Kaduna-based Future Africa Football Academy and then transferred to Football Academy, Abuja, where they were sighted by scouts during a tour of Europe.