The orders are the equivalent of the druid "subclass", but what set them appart from most other subclass is the ability to pick multiple of them, thanks to the order explorer feat, giving the druid access to a great amount of customisation. However, one big point of contention is that the "evolution" of these order aren't automatical as the druid level increase, but rely on spending class feat to keep the order feature relevant through the level range. Because of this, druids are somewhat limited in their feat choice, doubly so if they "double dip" through order explorer. Another issue is that the orders do not interact with each other, giving the druid little reason to "commit" to multiple order, and thus greatly reduce their future choice of class feat as they will need to "feed" each of them to keep them relevant.
This homebrew is thus an attempt to give some payoff for druids of multiple orders, by making them interact with each other, to make order explorer a more interesting option to build around.
Ancient Orders are "mid game" orders accessible only via a level 10 feat, that require the druid to already have picked the "order explorer" feat (and thus to belong to at least two orders). Each allow the druid to pick a bonus feat of level 8 or less amongst those that require their specific order to get access to, give a "payoff" that link both of the orders together, and open access to a short list of "Ancient order feat". Here's a few of those I though about so far :
Life Order Initiate FEAT 10
requirement : animal order, leaf order (or variant of either order), order explorer
You are initated to the secrets of the ancient druidic circle that considered all life as equal and worthy of protection. Your leshy familiar can Ride you or your animal companion without any penalty to either of them, as long as you and your companion are at least one size larger than your familiar. If your animal companion is larger than you and have the "mount" special ability, you both can ride it without any penalty. Your leshy familiar treat difficult caused by plant or fungus as normal terrain, and greater difficult terrain caused by such spells as difficult terrain, even if they were magically created. Any creature it mount also gain these benefits. If you have the "Woodland Stride" feat, you and your animal companion gain this benefit even if your leshy isn't Riding you.
You gain one of the following as bonus feat : Incredible Companion, Floral Restoration, Order Magic.
Special : If you belong to a variant order, you may instead take a level 6 or 8 feat that require that variant instead of the listed bonus feat. The feats "Grown of Oak" and "Garland Spell" affect your animal companion as if it was a leshy familiar.
Three of One Mind (1 action) Feat 12
Requirement : Life Order Initiate
You and your companions understand each other at a deeper level. You can use this action to Command both your animal companion and Leshy familiar at once, allowing both of them to use two actions, in any order.
Special : If you have the Call of the Wild feat, your leshy familiar can use it's inner magic to Sustain a Summon Animal or Summon Plant or Fungus spell you casted, as long as you Commanded it this turn. Creature that can perceive magic can sense that the magic is comming from it, and may act accordingly.
Archdruid of life FEAT 18
Requirement : Life Order Initiate
You understand the deepest secrets of this ancient circle, and your companions with you. Your leshy familiar and animal companion become immune to damage from spells you cast with the plant or fungus trait. Your leshy familiar can Ride any greature at least one size greater than it without imparting any penalty. Your leshy familiar now treat any difficult, greater difficult or hazardous terrain caused by plant or fungus as normal terrain, even if they were magically created. Any creature your leshy familiar ride gain these benefits. If you have the "Woodland stride" feat, you and your animal companion gain these benefits even if your leshy familiar isn't riding you.
Sky Order Initiate FEAT 10
requirement : storm order, animal order (or variant of either order), order explorer
You are initated to the secrets of the ancient druidic circle that looked up to the sky and saw the wind as an ally. Whenever you gain a fly speed (or as long as you don't lose your flight speed if you naturally have one), your animal companion gain a fly speed equal to it's land speed or Swim speed, whatever is greater. If it naturally have a flight speed equal or greater than it's land speed or Swim speed, it instead gain one more action each round, which it can use only to Fly. If your animal normally have no fly speed, then it must end it's turn on solid ground, or start falling.
You gain one of the following as bonus feat : Incredible Companion, Wind Caller, Order Magic.
Special : If you belong to a variant order, you may instead take a level 6 or 8 feat that require that variant instead of the listed bonus feat. If you have the "Storm Retribution" feat, that reaction can also trigger if an opponent that is at most 30 feet away from you critically hit your animal companion with a melee weapon or an unarmed melee attack, and the forced movement is based on your companion position instead of yours.
Wind and Talon, Fangs and Lightings FEAT 12
The learned how to talk to the wind, and it carry your command. Whenever you cast a spell after using an action with the spellshape trait that cost at least one action, you can Command your animal companion with a free action.
Special : If you have the Call of the Wild feat, you can instead Sustain a Summon Animal spell with a free action. If you have the Primal Summon feat, you can Sustain any Summoned creature with the Air trait as well.
Archdruid of the Sky FEAT 18
You have learned the deepest secret of this ancient circle, and your companion have learned to play with the wind and storm you conjure. Whenever you deal electricity damage to a creature, your animal companion consider them off guard until the end of your turn. Whenever your animal companion successfully strike, grapple, push or disarm a creature, they receive a -2 malus to their saves and are considered off guard against your spells with the air or electricity trait until the end of your turn.