If player A play a 6 and then player B play a 7 and finally player A play another 6, considering that each player put their cards in their own stack, would the two 6 will be considering as a pair?
No. The two sixes would not be counted as a pair. The pair needs to be with the last two cards played.
Pair: For adding a card of the same rank as the card just played Peg 2