Lawyers told the BBC that many families were persuaded to sign forms preventing them from taking legal action.
BBC Panorama has discovered that other relatives signed similar agreements after two other crashes, stopping them from suing Boeing in the US courts.
Boeing has declined to comment on the agreements.
All 189 passengers and crew died when the Boeing 737 Max crashed into the sea just 13 minutes after taking off from the Indonesian capital, Jakarta, on 29 October 2018.
Within weeks, relatives were offered compensation by insurance lawyers.
To access the money, families had to sign agreements that would prevent them from taking legal action against Boeing or the airline, Lion Air.
Merdian Agustin's husband, Eka, was killed in the crash. She says the insurance lawyers tried to pressure her into signing away her rights.
"They give me some document to sign. The document said you can have the money but you can't sue Lion Air. You can't sue Boeing.
"They said you should sign this. You should move forward. In one hour or two hours you will get the money and you will continue life, but I don't want it. It's not about the money. It's about my husband's life", she said.