A father and his son who saw the new moon should go [to beis din]; not that they can be paired together [as witnesses], but [so that] if one of them is disqualified, the second may be paired with another.  R’ Shimon says: A father and his son, and all rela- tives are eligible for testimony about the new moon.  Said R’ Yose, “It happened that Toviah the physician saw the new moon in Jerusalem —- he, his son, and his freed slave; and the Kohanim accepted him and his son, and disqualified his slave. But when they came before the beis din, they accepted him and his slave, and disqualified his son.”