The youngsters aged 13 and 14 and four other children, were discovered at a house in Gregg House Road in Shiregreen.
The four other children, aged 11-years-old, 10-years-old, three-years-old and seven-months-old remain in hospital.
The road was cordoned off as crime scene investigators carried out intense searches of the property.
Examiners are back at the scene today Saturday May 25, 2019 and tests are due to be carried out to find how the two boys died.
A 37-year-old man and a 34-year-old woman have been arrested on suspicion of murder in connection with the incident and remain in custody.
Specialist support officers are with the family.
Anyone with concerns or information is asked to call 101 or Crimestoppers anonymously on 0800 555111 quoting incident number 122 of 24 May 2019.