Dentist Mario Yela, 48, imprisoned at Pollsmoor Prison's hospital section, made an appearance at the Wynberg Magistrate's Court on Tuesday.
He is accused of murdering his son and daughter while exercising his visitation rights over Easter.
The request by his lawyer, William Booth, to have him housed in a single cell was denied.
Booth said Yela was constantly interrupted by correctional services officials while in consultation with his psychiatrist Tuvich Zabow.
Pollsmoor Prison, where Yela is being held, is also overcrowded and conditions are not conducive to healing, the court heard.
Yela was injured, allegedly while in police custody, and Booth's earlier request to have his client remanded to Victoria Hospital under police guard was denied.
Yela had written a letter to prison authorities complaining that he couldn't think properly or sleep because of the noise and his fellow awaiting trial inmates smoked, said State prosecutor Louise Freister Sampson.
Booth argued that his client was not given adequate time or a venue for proper mental assessment to take place and that a cell of 25 inmates was too much for him.
The matter was postponed until 10 May for the completion of a mental assessment to determine whether he is fit for court proceedings.