Oooh I like the first one. Okay, the way I see it is that the bullet will NOT get through the armor for the simple fact that the armor is absolutely bullet-proof whereas the bullet can get through "any" barrier... I'd rather go with the absolute option than the vague one. As for the second one I'm gonna look on it with a spiritual concept and say that if you believe in any sort of afterlife then yes, the man can drown in the fountain of eternal life. He'll only die and then live on in the afterlife anyway.
Not a problem. God creates a pebble and then declares "I shall never pick it up". He is capable of lifting it, but can not break his promise. Conditions met. Makes perfect sense. The bible says that God can never go against his Word which makes his Word more powerful than him. He can't break a promise, therefore he'd be bound by saying "I will never lift this stone." He's fully capable, just bound by his own Word
#4 doesn't actually work. See, when the girl goes "into the past" she can literally time travel back a day or even an hour. Having her grandmother die a day before the circumstantial "today" doesn't change the course of history (possibly the future but not the past) and therefore either way the girl was never not born.