Sounds like this is your in-law's properties. Do they want you to be their property manager? If no, then encourage them to find a different property manager. But it won't be you.
Otherwise, there's tons of resources out there about how to manage rentals. The real estate section here to start with. google will produce thousands of pages I'm sure. Bogleheads probably has a bunch. I know I've seen stuff on Reddit. Start reading.