The Ya’avetz rules (Sheilos 155) that in our day and age, having suffered so many long years of galus, we cannot be absolutely certain of the yichus [lineage] of any individual Kohen. It is therefore fitting that the Kohen returns the redemption fee to the father. In fact, sefer Otzar HaKohanim reports (end of Sukkah) that more than 1,000 years ago Eliyahu Hanavi appeared to Rav Hai Gaon and pointed at a group of alleged Kohanim who had gathered in a circle around the Mount of Olives on Sukkos – as was their custom every year -- and told him that only one of them was a genuine kosher Kohen.
Furthermore, the Ya’avetz rules that since most Kohanim are not necessarily kosher Kohanim, the father should try to find as many Kohanim as possible to redeem his son, so as to increase his chances that one will be a real Kohen. Since he rules that it is proper for the Kohen to return the redemption fee, the father does not lose anything by involving several Kohanim in the mitzvah.
However, most poskim deem it unnecessary to suspect the yichus of Kohanim (See Responsa, Chasam Sofer Yoreh Deah 291) and therefore recommend against asking more than one Kohen to do the ceremony. They also oppose the idea of the Kohen returning the redemption money to the father. The Minchas Yitzchok says (II 30) that one who uses more than one Kohen for the ceremony might make a beracha each time and run the risk of saying a beracha in vain. In sefer Teshuvos V’Hanhagos (I 658), it is written that leaving the redemption money with the Kohen is a segulah for the health of the baby.
On the matter of yichus, it is interesting to note that according to genetic research conducted in England by Oxford University and the University College in London, 80% of those who identified themselves as Kohanim shared a common gene that is found in only five percent of the general population. This research included Kohanim from all over the world – Ashkenazim, Sefardim and Yemenites. It is a strong indication that even in our day, there is basis for concluding that most Kohanim are indeed descendants of the Priestly tribe.
