I assume next round of Chatham Cup will see the 2 Mainland teams in a draw with the two Dndn teams? One team will be in the box seat to move through to next round.
Here the are rules (Regulation 12) regarding the Chatham Cup draw, these were updated in April this year.
4. COMPETITION FORMAT
4.1. All teams that have entered this competition shall compete on a knockout basis until two teams remain unbeaten.
4.2. NZF shall set the Competition Calendar on which the successive rounds of the competition will be held, or the day by which one or more rounds must be completed. Games must be played on the dates specified unless otherwise approved NZF or its nominee.
4.3. The draw for the rounds involving 32 and 16 teams (Rounds 3 and 4) shall so far is practicable have due regard for the costs of travel for participating teams, and desirability of promoting matches of such importance throughout New Zealand in order to maximise local and community involvement. For clarity the practical application of this regulation means that teams from within District Federations 1, 2 and 3 could be drawn against each other, as could teams from Federations 3 and 4, 4 and 5 and 6 and 7.
4.4. The competition will become an open draw from the quarter final stage with teams being required to travel, at their cost, throughout New Zealand.
4.5. All entrants shall be available from the Preliminary Round. The number playing in each round shall be: Qualifying Round as necessary to provide the required number of teams for Round 1. Round 1 not more than 128 teams Round 2 not more than 64 teams Round 3 not more than 32 teams Round 4 not more than 16 teams Quarterfinals not more than 8 teams
4.6. NZF shall be responsible for the draw for all games. The draw for each regional section of this competition shall be as NZF directs. The draw for the regional section of the competition shall have due regard to the costs of travel of participating teams. NZF shall, after each draw is made, advise each District Federation of the details of the games to be played and each Federation shall be responsible for notifying the teams respectively.
4.7. All teams competing in the competition shall observe the rules of the competition and any directions given by NZF concerning the promotion and conduct of matches.
4.8. NZF may at its discretion determine that certain teams do not enter the competition until later rounds.