What is the ruling on the Samaritan ritual that includes singing and drumming to summon jinn and dance with them? And what is the ruling on plucking armpit hair, and is there sin in shaving the armpit with a razor?

The impermissible singing is that which is accompanied by music, or takes place between non-mahram genders, or leads to intermingling, or involves squandering money and neglecting duties, or contains forbidden words, even if it does not involve summoning jinn. As for dealing with jinn, it is absolutely impermissible, even if the one doing it claims to use them for good. Therefore, the "Samiri" (a type of incantation or practice related to jinn, usually involving singing or chanting) with these characteristics is not permissible. As for removing underarm hair, the Sunnah is plucking, but there is no harm in removing it by any other method.