The crest you have is that of the 85th Field Artillery Battalion. Constituted in June 1916 as 2d Squadron, 19th Cavalry and organized in May 1917, the battalion was redesignated 2d Battalion, 77th Artillery in November of that year. Served in France with the 4th Division. Redesignated 631st Field Artillery Battalion in February 1944. Participated in the Invasion of Sicily and served in Italy for the remainder of World War II. Inactivated at Florence, Italy in September 1945. Redesignated 85th Field Artillery Battalion in November 1946. Reactivated at Fort Riley, Kansas in July 1948. Inactivated in Germany in July 1957. Consolidated with 77th Artillery in June 1958.
The cactus above the battlements commemorates the battalion's service on the Mexican Border in early 1917. Objects on the lower part of the crest are fleurs-de-lis representing the battalion's five major campaigns in France during World War I. Most of these crests were designed by the Army's Institute of Heraldry and this one is an excellent example of their work. The words on the scroll is the battalion's motto.
The battalion was active during both periods of service - your Dad's and your brother's. Most likely it's your brother's.