Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos) By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
74. It is a negative commandment for a court “do not accept the testimony of a relative”
As it states in Devarim (Deuteronomy) 24:16, “do not put fathers to death because of children.” This means through the testimony of children. The same law applies for other relatives.