Rosh Hashana 1:6

On one occasion, more than 40 pairs of witnesses came on Shabbos, so Rabbi Akiva detained them in Lod. Rabban Gamliel notified Rabbi Akiva that he should not detain unnecessary witnesses because that will discourage them from coming in the future when they may be needed.

Rosh Hashana 1:7

If a father and son (who cannot testify together) both saw the new moon, they should both go to testify – not because their testimony will be combined (it won’t) but because one of them might be disqualified, in which case the other’s testimony might be joined with that of another witness. Rabbi Shimon said that a father, son and all relatives can combine their testimonies about the new moon. Rabbi Yosi said that, on one occasion, Toviah the physician, his son and his freed slave all saw the new moon in Jerusalem. The Kohanim accepted the testimony of Toviah and his son together but not that of the freed slave. When they came to testify, the court accepted the testimony of Toviah and his freed slave but not that of his son.