The pair were found in Dryden Lodge in the suburb of Grey Lynn on Tuesday.
Police say Ellwood (39) and Hamiton (36) were known to each other and are not looking for anyone else in relation to the matter.
Ellwood had been missing for more than a week after last being seen in Newmarket on Wednesday 28 February.
Police would still like to hear from anyone who may have seen or had contact with Ellwood or Kerr after 11am that day.
A horrified maintenance worker discovered the bodies. As police scoured Dryden Lodge yesterday, the man was too emotionally overwhelmed to speak.
Police were called to Dryden Lodge, which operates as a halfway house for many tenants with drug and alcohol problems, at 3.15pm on Tuesday.
Upon arrival, they found two people dead. Detectives were working to establish what happened.
Yesterday the downstairs level of the Grey Lynn property had been partially cordoned off. Inside the cordon were single bedrooms and a kitchen, resident James Davidson said.
Police were donning face masks and scrubs to enter the cordon. Some residents had been evacuated.
Davidson has lived in the lodge for two years. He told the Herald he woke from an afternoon nap on Tuesday to find police everywhere.
He didn't know the people who had died but said a lot of the lodge residents had alcohol and drug issues.
A room at the lodge costs between $200 and $400 a week, Davidson said.
A woman who works in an office a few doors down said police were often called to the lodge as it was a "colourful area". She wasn't surprised to hear of the double death because of all the drugs around but hoped it wasn't malicious.
"Hopefully it's not a nasty murder."
The landlord said "my tenants have been through a lot" but declined to comment further.
The discovery of the bodies followed a police appeal to the public on Tuesday morning to help find Ellwood, saying they were concerned for her safety.
She was last seen in Newmarket about 9.30am on February 28. Police described her as being of slim to medium build, 166cm tall, with long blonde hair.
Ellwood is believed to live around the Dominion Rd, Sandringham-Mt Eden area, and her parents are based in Remuera.
She last contacted family at 6pm on February 27, and it was said to be out of character for her not to be in contact.
A family member posted to Facebook on Tuesday saying: "We love you Tania and we will find you."
Ellwood is listed on StarNow as being an actor, hair stylist, makeup artist and fashion stylist. She had a brief stint on Shortland Street where she played a character called Mandy Timmins.
