The couple, aged 29 and 23, have been charged with murder and aggravated assault, the Swedish Prosecution Authority said in a press release.
The woman is believed to have been murdered on the night of June 13 in the couple's home. Four days later, she was reported missing by her son. She was later found dead in a lake.
"I believe they both planned to kill the woman, and that is why they invited her to the apartment," prosecutor Johanna Stigson said in a comment.
They are also charged with conspiracy to murder another of the man's relatives.
Among the evidence is a picture on the 23-year-old's mobile phone showing a bundle in a lake. When police examined the object, they found the deceased woman. Investigators have not been able to determine how the woman died.
