It is clearly stated, in the mission Paradox. At one point Preadyth says, "I came into the Vault with two others." Makes no sense for him to acknowledge 2 of his teammates abd ignore the other 3, so it's safe to assume there were only 3 of them.
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It is possible they were wiped from time
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Unless it was a situation like Kabr knowing he had to have entered with other members of a fireteam, but not being able to remember them
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Edited by rZI3: 4/29/2016 5:44:17 PMBut remember that mission that we collect the ghost, we enter the vault as a max 3 man team, where all the vex are frozen out side