The 17-year-old had been arrested by police yesterday, while the 18-year-old later went to a station himself following an appeal by officers.
Both were released after questioning, with further investigations underway.
Police are still looking for a third teenage boy, who they believe was involved in the incident.
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An altercation broke out between two groups at a Sunshine bus stop on May 18, where 16-year-old Lyhym was fatally stabbed, and two more teenagers of the same age were injured.
Police are still investigating the circumstances of the incident.
