Their bodies were found by a caregiver at about 7am when she went to check on them as she had last heard from them on Thursday.
Police spokesperson Colonel Priscilla Naidu said the caregiver had to get a security guard to open the door of the house.
“They opened the house and found the couple in the bathtub.”
She said the woman, 79, had multiple stab wounds.
The man, 81, had no visible signs of injuries.
Naidu said the couple could not be named until their next of kin had been notified and the bodies identified.
“Nothing was taken from the house and there were no signs of forced entry,” she said.
All the doors and windows were locked.