They should be killed, so that their message would not pollute the people.
They should be let go; if their message was from men it would fail, but if it was from God it could not be stopped.
Nothing should be done to them because Gamaliel had been told in a dream that their message was true and that they must not be harmed.
They should appear before the people to publicly debate their message with the Pharisees.
They should be thrown into prison indefinitely.