First of all, Mazal Tov on your cousin's Bar Mitzvah! The average Torah Scroll weighs abound 20 to 25 pounds. The heaviest is about 50 pounds. There are some "minis" that weigh about five pounds. These small Torahs were usually written for Chassidic Rabbis. Older Torah Scrolls are usually larger and heavier.
Your father might try getting to the synagogue early and taking the Torah Scroll out for a "test drive." No one ever died from getting to synagogue early!