I can't say specifically about Orlanthi, but did writeup customs for Imtherian marriages years ago. I actually ran a whole marriage ceremony (including the gift-giving in advance) - the mystery was trying to discovery who the Trickster was.
Imtherian Marriage Customs:
Local villages come together during Fire Season for several purposes, including socializing, rituals to invoke the power of Khelmal (which require groups of disparate people to get together for common aid), and introducing young people from the different villages.
Marriages are arranged by the parents, though often youthful appeal plays a part (at least in getting the child to state her/his preference to their parents). About 95% of all marriages are between people of differing villages--marriage within the village is frowned on and considered bad luck (several stories point this out--the marriage of Khalana and Basmal is a mythic point; the marriage of Delea and Voshon is a common folk tale).
Marriages are arranged usually to occur in Storm Season (it's considered best luck to come together at that time) or Earth Season (for those in a rush the time of good harvest is considered well-omened). Dark Season marriages are bad luck and ill-omened (the mythic marriage of Queen Balurga whose husband was then sacrificed is the classic example).
To seal the marriage, the parents exchange cheeses (always brought along for these festivals if they have marriageable children). Once each season thereafter, until the marriage, the prospective groom and bride send gifts to each other. These are expected to be tokens of their coming love and are usually common crafted gifts (woodcarvings, musical instruments, necklaces, or foodstuffs like cheese or casks of cider). The gifts are always taken to the other through someone not of the family (the prospective bride and groom try to avoid having a Trickster or Keeper of Dire Secrets bring these, however, since the former love to substitute other gifts and the latter always add their own prophetic gifts).
During the period between arrangement and marriage, the prospective groom must prepare a new hearth for himself and his bride. This may be as simple as digging a new fire pit in his parent's dwelling or as complex as building his own dwelling including the fire pit. The fire pit/hearth always includes a hearth gift made to Ralaska to bless the marriage to come. If his parents are dead and he has possession of their former dwelling, then he must rebuild the hearth by removing his parent's hearth gift and replacing it with one of his own.
When the day of marriage is at hand, the bride's parents assemble gifts for the groom, the groom's parents, and the groom's village. For the latter, a barrel of cider is customary, but could be apples, cheeses, a boar for roasting, etc. When the gifts are ready, the bride is placed upon the cart and with Lokarma's blessing for a gentle trip, the bride travels to her new village.
The bride departs from her home upon the bridal cart, which contains the bridal gifts, the bride's personal dowry, and decorations of seasonal flowers or branches. Any animals that are part of the dowry trail behind the cart. The bride's personal dowry usually consists of assorted goods for her new kitchen: a bronze or copper soup pot; earthenware bowls and mugs; spoons (commonly wooden--bronze or copper if the family can afford them); a bronze ladle; a candle holder (or an oil lamp if possible); carvings of Nealda (for fertility), Imthus and Aidea (for good health and marriage), and Ralaska (for a warm hearth); a covered brazier containing a hot coal from her parent's hearth; and assorted pins and braid ornaments (richer farmwives might also have passed on rings, necklaces, armrings, or earrings to their daughters).
As for the decorations, for Storm Season marriages, villagers make wreaths of Ryar’s Boughs--enduring branches of the stately fir tree. For Earth Season marriages, villagers use wreaths of Aidea's Stars, the vivid white three-petal flower which blooms three times a year. The rarer, but joyous, Fire Season marriages use a mixture of flowers, usually including Aidea's Stars, Cat's Eyes (a fine yellow flower with a brown center), Dendara's Hair (whose yellow flowers amidst willowy leaves give the effect of finely decorated hair), or Yelem's Mantle (a large petal yellow-orange flower).
The bride is accompanied by her parents, siblings, other relatives, close friends, and a village representative to the new village. All of these, but two (one chosen to be the cart driver), must walk beside the cart. If a Khalana healer is in the party, (s)he may also sit in the cart and play upon her ousa. Otherwise, the bride's best friend sits in the cart with her and helps her braid her hair.
When the bridal party has reached their destination, they are greeted by the headman of the groom's village or his representative. The headman leads the party to the town circle and ritually welcomes the bride into the village. He usually repeats the a formal greeting while young children holding hands dance around the cart.
The bride responds by tossing a garland or wreath from the cart to the dancing children. Whoever catches the wreath is supposed to always have good luck henceforth upon that day of the year. The headman assists the bride to descend from the cart and leads her (with her relatives and assorted local children trailing behind) to the groom's home. The gift of the bride's parents is then made to the groom's parents. When the groom's parents have accepted the gift, they present their son, the groom to the bridal party and pronounce their own greeting.
(Note: the post-marriage feast typically takes place upon a raised platform or stage within the village hall or on the village common. This is supposed to bring the party closer symbolically to Arahar and Teliska who made the first marriage.)
Once the presentation of the bride and groom is complete, the village headman leads the entire party to the local shrine (this may be a common shrine to all deities or one devoted solely to Imthus and Aidea). There the priest and priestess of Imthus and Aidea (or in rarer cases those of Arahar and Teliska or Khelmal and Nealda) bless the union and pronounce the marriage vows. The priest and priestess light two candles and place them upon the ground. The new couple must dance around the candles hand-in-hand ten times for good luck (five times one way and then five times the reverse).
Note: it is a bad omen to knock a candle over; to have a candle go out is very bad luck--one of the partners is sure to die young.
The priest and priestess then join the new couple in a second dance to link the new marriage to all past marriages in a continuum from Arahar and Teliska to the present.