None *et al.*
Doesn't matter. Lightbulb is going to die anyway.
Two, but I don't know how they got in there.
Two: One to change it, and the other one to change it back again.
Six. One to change the bulb, and five to hug and kiss him.
They have the ability to penetrate both holes at the same time. explanation(http://en.m.wikipedia.org/wiki/Double-slitexperiment)
Urea!