A. From the word echod - one. Brothers are as one. Either in the sense of relationships or in the sense of doing Mitzvos.
Q. How many types of people are there that are disqualified from serving as witnesses ?
A. 10. Rambam
Q. May a convert serve as a witness ?
Q. How many places in Shas does the Halacha follow Reish Lokish ?
A. 3 places.
Now may be a good time for a gem of Torah study.