The six and seven-year-old boys were found dead at a property at Coonabarabran, in the NSW Central West, at 2pm on Monday.
Their 66-year-old maternal grandmother, who was their sole carer, was found by police with self-inflicted injuries and was arrested at the scene.
A message sent to the communities and justice department triggered the police response but the force would not confirm reports it came from the grandmother.
Assistant Commissioner Andrew Holland said the grandmother was in hospital being treated for her injuries and undergoing a mental health assessment.
"Based on that information, we'll make some further inquiries (and) hopefully by the end of (Tuesday) afternoon, we'll have some further updates for where we're at with the investigation," he told 2GB.
"We expect charges to be laid, most definitely … we're just depending on the results of those assessments from the medical practitioners."
Mr Holland said the police involved, along with the Coonabarabran community, were distressed by the death.
"The sight of a six and seven-year-old boy deceased inside a house, and then the (grand)mother inside as well with self-inflicted injuries, is confronting for anyone," he said.
"In regional areas, any deaths affect a small community (and) the death of two innocent children will have a long-lasting impact."
The deaths are being investigated under Strike Force Darnum, assisted by detectives from State Crime Command's Homicide Squad.
Local MP for the NSW electorate of Barwon, Roy Butler, acknowledged the tragedy on Facebook, saying his heart went out to the local community.
"The death of any child is always devastating. In a small, close community, where everyone is connected in some way, it hits the community even harder," he said.
"Any death is tragic, but in circumstances where it's avoidable, it causes even more pain."
Premier Chris Minns said the education department was working closely with the boys' school to provide support to other students.
"These are the kinds of crimes that are just so heartbreaking for a community like that, to think of the vulnerability of young children in particular, I can imagine that community is going through hell right now," he said.
"We'll provide all of the resources and help that we can, either through the school or the local community, but I'm heartbroken for them, and I realise this will leave and cast a long shadow."
Mr Minns declined to offer further comment on the matter at risk of compromising the police investigation.
The news has rocked the close-knit agricultural community located 140km north-east of Dubbo, with a population of about 2400.
Police will address media on Tuesday afternoon.
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