Grandpa scammed into giving computer access, how to lock him down again?

Hi! My father-in-law (78 years old) got a phone call last night from some “company” claiming that they detected an issue with the hard drive on his computer and they wanted to help him fix it. He bought that line completely and followed instructions to give the scammer remote access. His son came in the room and noticed the cursor moving on it’s own and someone was accessing the command prompt. He promptly unplugged and turned off the laptop. But, we don’t know what damage was done. In that house, there is a modem, wireless router, a desktop PC (the son’s) and the old man’s laptop. What should be done to lock this down? Virus an malware scans on the old man’s laptop, at a minimum. But what else? To target him like that tends to point to identity theft on some level. They knew his name and home phone number.