Let's say I breed:
Toterra (Male): Leech Seed, Stealth Rock, Seed Bomb
What order will the egg moves (Leech Seed, Stealth Rock, Seed Bomb) replace Ferroseed's start up moves (Tackle, Harden)?
Actually in Breeding, it's all Random from IVs to Egg Moves. There will be no order that you will receive your Egg Moves, it's all random. For example with your Pokemon and Moves, you will receive your Moves from random, so sometimes Harden or Tackle on Ferroseed, sometimes No Leech Seed.