Two questions about how the en passant capture works I am still confused about the en passant rule. There are two possibilities regarding the capture itself that are not clear to me.
[FEN &quot;&quot;]
1. d4 d6 2. d5 c5 3. dxc6 b5 (3. c4 e5 4. dxc6)

Scenario 1: In main line shown above, is it possible to capture via en passant again after 3... b5 with the move 4. cxb7ep? In other words, is it possible to capture en passant twice with the same pawn?
Scenario 2: As shown in the given side variation, is it actually possible to capture the black’s pawn on a later move? Note that although the black pawn is still in the diagram, you must imagine that it isn’t.
En passant can only be played when the enemy pawn moves over your pawn's capture square during it's first move (moving 2 squares); so the answer to both condition 1 and 2 is no.  

It is not possible for a pawn to en passant twice in a row.

My understanding is in early chess pawns could only move one space at a time, so when the 2 move rules was added they also added en passant to counterbalance the fact that you might lose a chance at capturing your opponent's pawn since he could now move over your capture square.

So, in essence, because after capturing en passant it is no longer possible for an enemy pawn to pass over your capture square, it is no longer possible for your pawn to capture en passant.

The official FIDE rules, article 1 section 3.7d states:


  A pawn attacking a square crossed by an opponent’s pawn which
  has advanced two squares in one move from its original square may
  capture this opponent’s pawn as though the latter had been moved only
  one square. This capture is only legal on the move following this
  advance and is called an ‘en passant’ capture.