Mr Kuczynski and his sister-in-law Ms Sukpengpanao both died of stab wounds.
Results from a post-mortem examination showed Ms Sukpengpanao, who was visiting the house at the time of the deaths, was killed by stab wounds to her neck.
Mr Kuczynski, who was living in the house with the two girls, died of a single stab wound to the neck.
Post-mortem examinations carried out later on Jasmin and Natasha found they had also died of knife wounds to the neck.
Detectives are not looking for anyone else in connection with the deaths.
