The tax implications will probably determine if or how you can keep all the properties. The lawyer should have many suggestions as to how to proceed. It will be a full time job to oversee these assets and learn at the same time. Be cautious now when someone wants power of attorney that it only applies to the job at hand.
Assuming you keep them and your Grandfather had no management companies, I would get 3 different ("a man should know his limitations") management companies, one for each building. As time moves on and you learn more, begin to be more "hands on" with the least performing company until you think it's time to replace them or step in yourself. If they all do well, accept yes for the answer and keep them all. If your Grandfather has records of who he dealt with for contractors, finances, advertising, and so on, get copies of those records.
You'll have your hands full with the attorney, accountant, and checking on the management companies. They're all only human so check often and be prepared to change them as necessary.
Jim