2-point conversion, interception, then a fumble, then a score

Question: If, as at the end of the Denver/New England game, the final 2-point conversion attempt was intercepted in the end zone (it was), and the player who intercepted the ball fumbled (he did) and the fumble was recovered - would:
- First, let's back up a step, if the player who intercepted the ball for Denver had run it back to the other end zone, would Denver have scored 2 points or 6 points? As I looked up the rule, that Denver would have only scored 2 points ... right?
- Back to the original question, if the player for Denver had fumbled and a New England player had picked up the fumble, could that New England player have advanced the ball, and, if so, would that have been for 2 points or, due to the change of possession to Denver, and the following change of possession to New England had turned that into a 6 point touchdown?

I read the rules on the above and, not being a big time NFL fan who 'knows the rules', it seems to me that the NFL rule book leaves the second question above open, but does answer the first question above.

What would the ruling on the field be for the first question?

What would the ruling on the field be for the second question?