The defendants were reported to the judicial authorities by an anonymous neighbour. This is the first FGM-related conviction in Guinea Bissau since the country prohibited the practice in 2011.
Six people were originally tried for female circumcision. The defendants said the FGM practice is in keeping with their Islamic faith.
The government-run National Committee for the Abandonment of Harmful Practices, which brought the complaint, said it hoped the group would get long sentences.
The committee’s spokesman Fatima Djau Balde said he hoped the prosecutions would “be a lesson to those still thinking of perpetuating this harmful and retrograde practice”.
Female genital mutilation (FGM) is usually carried out on girls between infancy and age 15. It can cause infections and, later, infertility and childbirth complications.
According to a health ministry report released in 2012, at least 320,000 women and young girls have undergone FGM in the nation of 1.7 million.
It said the practice was most widespread among Muslim communities such as the Mandinka and Fula and Biafada.
The Bissau-Guinean parliament passed a law in June 2011 banning FGM and making it a crime punishable by up to five years imprisonment.
The maximum penalty is five years in prison and a fine of 500,000 CFA francs ($95, 76 euros).
Aid agency Plan International said earlier this year 50 percent of girls continue to be victims.