Complex sentence: Jack was the son of Tim Mara and brother of Wellington, and served as the team's president for 31 years, in addition to becoming co-owner upon the death of his father in 1959.
Split into simpler sentences: Jack was the son of Tim Mara and brother of Wellington, and served as the team's president for 31 years. He became co-owner of the team along with Wellington upon the death of his father in 1959.