Tegan Jovanka held possession of a TARDIS key, given to her by the Fifth Doctor. (AUDIO: Hexagora) She had previously been without one and was given the Doctor's spare key in the event she was separated from the group on Monarch's ship. (TV: Four to Doomsday)
Tegan nor Vislor Turlough were in possession of a TARDIS key when Kamelion began travelling in the TARDIS. The Doctor gave them a spare before they were separated on Mekalion. (AUDIO: Devil in the Mist)