Chad Grossmann tells WISC-TV the victims were both "just wonderful people." He recalled how his mother, Robin, loved birds and squirrels, and how his sister, Charity, loved to laugh.
The victims were killed May 2. Chad's teenage brother was injured and briefly hospitalized.
Madison police say Londrell Johnson stabbed the women, and still had the knife in his hand when an officer shot and killed him.
Chad Grossmann says he forgives Johnson, who was mentally ill and on medication. Grossmann says he blames the lack of funding to help support the mentally ill.
The funerals for Robin and Charity Grossmann were set for Saturday morning.