Marlene's brothers were "Bob Quade, Tom Kennedy & Mark Thompson"
Note the surname "Quade" for Bob, which I'm presuming is the son Robert, and that the son Thomas was the Kennedy & that Mark was a Thompson, just as you stated.
So, by that, you are looking for Dorothy Quade, a Dorothy Thompson & a Dorothy Kennedy. Maybe you will have some luck with that Quade thrown in. Not quite as common as Thompson or Kennedy. (but yeah, you'll still be fighting off references of Hollywood and of politics...)
Here's Marlene's obit...
Grand Rapids Press, The (MI) - Wednesday, October 21, 2009
SCHOFIELD (Cedar Springs) - Mrs. Marlene Joy Schofield, age 70, went home to be with her Lord and Savior on Tuesday, October 20, 2009. In 1957 she graduated from Crandon High School and then earned an associate's degree in teaching. Bob, an early childhood sweetheart proposed to Marlene and they were married in Argonne, WI on June 3, 1961 with the word "always" engraved on their wedding rings. She taught school for a few years and then became a full-time wife and mother. Marlene taught her children to be kind, to love, and to be faithful to God and family. She enjoyed playing the piano, spending time with her family and spoiling her 11 grandchildren. Marlene is survived by her husband of 48 years who was her best friend and love, Bob; children, Tom (Ann) Schofield of Traverse City, John and Carrie Schofield of Ada, Julie and Stefan Swartzmiller of Madison, WI, Shelly and Kevin Mehring of Oregon, WI; grandchildren who lovingly called her "Gaga", Janelle, Stefan, Sarah, Christian, Lauren, Masen Schofield, Madison, Hannah, and Sophie Swartzmiller, Tyler and Trevor Mehring; brothers, Bob (Jan) Quade, Tom and Mary Kennedy, Mark Thompson; nieces and nephews; and in-laws, Daniel and Mary Fannin, Kathy and Daniel Trainor. The service for Marlene will be Saturday at 11:00 a.m. at First United Methodist Church of Greenville with the Rev. Steve Charnley officiating. Interment will be in Rockford Cemetery. Relatives and friends may meet with the family at the Pederson Funeral Home from 6 to 9 p.m. Friday and from 10 a.m. until the service at the church on Saturday. Pederson Funeral Home, Rockford
www.pedersonfuneralhome.com