Remorseless Punishment

• WWizards of the Coast2016-01-22
  Official Ruling
  No player may take any actions between the two times the player goes through the process.
• WWizards of the Coast2016-01-22
  Official Ruling
  Any abilities that trigger while Remorseless Punishment is resolving will be put on the stack after it has completely resolved.
• WWizards of the Coast2016-01-22
  Official Ruling
  The player can’t choose to discard two cards unless they have at least two cards in hand. Similarly, that player can’t choose to sacrifice a creature or planeswalker unless they control one. This means that if the target opponent doesn’t have two cards in hand and doesn’t control a creature or planeswalker, that player will lose 5 life and then lose 5 life again.
• WWizards of the Coast2016-04-08
  Official Ruling
  The same player chooses both times. In a multiplayer game, you can’t choose a different opponent to repeat the process.

Rulings via Scryfall