Kristopher Karolkiewicz, the father and husband, is believed to be the suspect in the murder-suicide, the sheriff's office said.
Authorities said Karolkiewicz started the fire in numerous places throughout the house after carrying out the murders.
"The cause and origin of the residential fire remains under investigation by Michigan State Police arson investigators. However, preliminary indications are that the fire was intentionally set in numerous places throughout the interior of the residence. The family pets also perished due to the fire/smoke," the sheriff's office said in a press release.
Amanda and her two adopted daughters had returned in mid-July from a vacation in China, where she took them to Shanghai Disneyland, according to her TikTok.
📩 Send me a story idea: Adam.Sabes@fox.com
➡️ X: @asabes10
The Grand Haven Fire Department initially responded to reports of people being able to smell smoke in that area between 8:30 a.m. and 9 a.m. on Friday, but firefighters couldn't locate a fire.
Amanda's stepfather, Steve Lawwill, wrote that he was "so grateful for the joy they brought into our life" and that the family is "just so shattered."
Just before 11:45 a.m., officials returned to the 14900 block of Riverside Trail after receiving reports of white smoke coming from a home there.
The Ottawa County Sheriff's Office said there are no additional suspects.