In which form should verbs following nominal phrases like "none of you", "either of you", etc. be?

The question of whether you should use neither is or neither are has been answered here and here.

As for the correct verb form after which in a question, it depends. If you want to refer to a singular person, you should ask "Which of you is...?" But if you want to refer to more than one person, then the plural form is acceptable, as in "Which of you are ready to follow me?" Note, however, that this form sounds a bit stilted; a more natural way to ask this question would be "Who is ready to follow me?"