Since we have the other two games to draw from, can we use additional decks from the other games or will it affect play balance if the mixing of two decks after the initial use of all four decks is not used......If we are to use the mixed decks then I also assume you keep recycling the other two decks into a mixed deck as the game continues, yes?
Don't get the context of the first part (underlined) of the question. I am assuming that you have multiple copies of the game - so have mutiple draw decks that could be used. If that is the case, can't comment on the impact of using additional draw decks.
Even if using the mixed deck method (as outlined in the rules) - the use of the two largest decks is simply to give a larger set of cards to be shuffled to make the new draw deck. As you continue to use cards, continue to sort them on discard by their backs. Anytime a new draw deck is needed, shuffle the two largest decks to give you the largest TC deck.