Complex sentence: The 4s, Aces and 7s are very disputed cards they are used differently by different people (usually their actions are interchanged) and when starting a game usually players agree what each card does.
Split into simpler sentences: The 4s, aces and 7s are very disputed cards once they are used differently by different players. Usually their actions are interchanged and when starting a game, players agree what each card does.