Five people were still in hospital yesterday morning in Nairobi but two of those were likely to be discharged later in the day.
Three are undergoing further tests.
Dr Johnston and his wife Grace, both of whom lived in Tauranga, former Bethlehem College student Caitlin Dickson, 19, and Kenyan driver Christopher Mmata were killed in the crash.
Dr Johnston had worked at Whakatane Hospital for the past five years, commuting from his Tauranga home.
The bodies of the three dead and at least four students have returned home.
Funeral services for the Johnstons and Ms Dickson will be held at the Bethlehem College events centre in Tauranga.
The Johnstons funeral will be held on Saturday at 10.30am, while Ms Dickson's funeral will be held tomorrow at 1.30pm.