The 22-year-old centre-back joins the Islanders on a three-year contract which will keep him at the club until 2023.
Nemil was sent to Spain last year to train with Marcet's High-Performance Academy in Spain by RFYC.
Mumbai City head coach Sergio Lobera described the Nigerian as a top-class player.
The 33-year-old Englishman joins the ISL side ahead of the 2020-21 season, bringing in tons of experience and quality to the Mumbai City FC attack.
Neville has had the experience of playing under new East Bengal coach Robbie Fowler at the Roars till last season.
The tests were conducted in Goa after the arrival of the teams and all of them are asymptomatic cases.
Newly-appointed East Bengal head coach they would aim to create a team which dominates ball possession.
The former Liverpool striker is expected to join the team in a week time in Goa ahead of the ISL season kick-off.
The seven members, including Spanish players Edu Garcia, Javi Hernandez and Tiri will undergo home quarantine for two weeks in Goa, according to a statement issued by ATK-MB.
With the club's foreign contingent still awaiting their visas, as many as 29 players attends the opening session, along with first-team Indian assistant coach Naushad Moosa.
Bhutia said the club would face difficulties in making up a squad and should look to build a team for the long-term.
Manchester United congratulate East Bengal on centenary celebrations and wish them good luck for much-anticipated ISL entry
Das also said the AIFF was delighted at East Bengal finally getting an investor, clearing the decks for the century-old club to enter the ISL from this season itself.
East Bengal on Wednesday got an investor in Kolkata-based Shree Cements and West Bengal Chief Minister Mamata Banerjee, who played a big role in the negotiations, made a strong pitch for the century-old club's inclusion in the ISL.
West Bengal Chief Minister Mamata Banerjee made the announcement on Wednesday, saying "all problems are solved, East Bengal will now play in the ISL".
West Bengal Chief Minister Mamata Banerjee on Thursday announced a joint venture between the century-old club with the city-based Shree Cement company.
Albert Roca has parted ways with Hyderabad FC to join Ronald Koeman at Barcelona.
Borussia Dortmund will focus on building and supporting HFC on its academy structure as well as guiding the Indian club on coach education.
With 59 appearances for CFC in all competitions so far, Sabia is preparing for a fourth season with the Marina Arena club by focusing on his fitness currently back home in Brazil.