Lufuno Maphiri, prosecuting, said the pair were being charged under the legal principle of common purpose.
He told the court: “The firearm, to date, has not been recovered,” adding that prosecutors believed it had “been concealed”.
Over the weekend, police told local media they believed the shooting stemmed from a labour dispute between the gardener and one of the suspects.
Bellarmine reportedly barricaded himself in his room when police arrived, but later co-operated after hours of talks.
He is also reported to have denied shooting the gardener and said the wounded man was in fact a security guard who shot himself.
The gardener was reportedly shot in the back and remains in hospital in a critical condition.
Neighbours have since said they heard gunshots coming from the property before last week’s incident.
Grace Mugabe, who lives in Singapore, did not attend her son’s case in court, which was postponed until March 3 when a bail application will be heard.
She faces arrest in South Africa after allegedly assaulting a 20-year-old model with an extension cord in 2017, when she found her in a hotel room with her two sons.
She denied the assault at the time and said she was acting in self-defence.
Most of Robert Mugabe’s family have moved abroad amid strained relations with his successor, Emmerson Mnangagwa, after accusing him of betraying the dictator’s legacy.
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