It appears (on the information given) that the police did neither: they didn't lawfully detain the suspects or control their actions through a legally authorized manner (e.g. arrest them, serve a warrant on them), but the police did restrict their actions (prevented them from entering the house).
It seems on the face of it that the police inhibited the victims' legal rights, without exercising a legally authorised reason to do so (or relied on misinformation to suppress the victims awareness of their legal right to choose to not comply with the police officers' requests).
The had a data point (albeit a poor one) that said a missing person was in their house. The officer told them to sit outside and not go back in. That's lawful detainment.
It seems on the face of it that the police inhibited the victims' legal rights, without exercising a legally authorised reason to do so (or relied on misinformation to suppress the victims awareness of their legal right to choose to not comply with the police officers' requests).