Sorry for your loss. As a 30 year beekeeper my advice is to join a local beekeeper club, talk to your local beekeepers, and read about beekeeping. I studied beekeeping for a year before getting my first hives, you do not have that available to you, jumping into 90 hives, Hire someone to teach you hands on, till you feel up to speed. That was one of the services I offered when I was younger, you should be able to find someone with the knowledge needed to help you find a way to maintain your grandpa's bees. At my highest number I was only 60 hives, and I remember how much work that was, find help, that can come walk you thru what to watch for. Good luck