1. Probably the threaded shank of the tap was shorter than that which was there before it, so female iron used as an extension.
2. Yes, to free the tap you would need to:
2a. Undo the tap connector compression nut (lowest hexagon).
2b. Remove the iron (still called an iron even though its brass) by undoing the middle (brass) hexagon.
2c. Remove the back nut - black plastic nut.
3. When fitting new tap:
3a. If it comes with a plastic back nut, worth replacing with a brass back nut. Less likely to split and gives better grip on tap.
3b. If the shank is too short to reach the tap you may need to re-use the iron.
3c. If you have to use the iron, you will almost certainly need to use PTFE tap, Loctite 55 or a liquid sealant like Loctite 577 or Flomasta Pipe Seal to seal the iron to the threaded tap shank.
3d. Get a new fibre washer (1/2" tap connector washer) for the tap connector.