en_tn/mrk/03/35.md

whoever does ... that person is

"those who do ... they are"

that person is my brother, and sister, and mother

This is a metaphor that means Jesus's disciples belong to Jesus's spiritual family. This is more important than belonging to his physical family. Alternate translation: "that person is like a brother, sister, or mother to me" (See: rc://en/ta/man/jit/figs-metaphor)