Chelsea and Vitesse agreed to Saiyabulang and Nathan will join the Dutch team on loan for a season.
18-year-old Brown can assume the role of a winger or striker, he shine in the 2014-15 season.
Last season he captained his team to participate in Youth U19 League, and in the final against Shakhtar when scored two goals, helping the team win. He also followed U18 team to participate in the FA Youth Cup, and scored in the second leg of the final, helping the team to beat Manchester City cup.
In February he was eligible for promotion to the first team of Jose Mourinho, and staged the first show in the league finale.
In addition to Brown, just on July 1 officially joined from Atletico Paranaense of Brazil players Nathan, the coming season will be leased to Vitesse.
The attacking midfielder has represented U17 and U20 international team play.