A house records where people came from. It owns nothing, commands nobody and never disappears from the record. A house is living while at least one of its members is alive. Its name becomes available to a new, separate house only after its last member dies or is adopted into another house.
You belong to the house you founded or were born into, and there is one way to change that: being adopted. A house is never applied to, joined by choice, resigned from or expelled from.
When you have no active character, you may choose either route on Account:
The pool belongs to the world. A parent has no exclusive right to play their child, and any player may later take the child who inherited your titles.
At twenty, one played character may propose to another played character. A proposal is made from the other character's page, the way a duel is: open them, and under Marriage the page offers the proposal or says which condition stops it, whether they are married, too young, dead, or played by nobody. The recipient answers from Account, where every proposal made to them and by them stands with accept, decline and withdraw. It never accepts itself through silence, and no liege approves or vetoes it.
A house's tree shows who is unmarried. The world keeps no roster of the marriageable; open a house under Rankings → Houses and each living, played member of age who is married to nobody is marked so, a widow among them, with their titles and claims beside the mark.
A person has at most one living spouse. Death ends the marriage; the surviving spouse may marry again. People of the same sex or different peoples may marry, but only an opposite-sex couple of the same people can have children.
The proposal chooses which house the children join, named as the two houses, yours and theirs. The record calls the two answers patrilineal (the father's house) and matrilineal (the mother's), and the account says which house the children of your marriage join. A couple who can have no children is not asked.
Once each player year, each eligible spouse rolls fertility and an eligible couple rolls once for a birth. A newborn is age zero, alive, unnamed and played by nobody. They are born where their mother stands and hold citizenship in their own people's homeland.
A newborn may be born with a trait, and may inherit a temperament from a parent; a gay spouse has children less often. See what you carry.
Either living parent may name an unnamed child from Account. The first name given is final. If neither parent chooses one within three days, the world chooses a name from that people's naming language so the child can appear in the pool. If both parents die first, the world names the orphan immediately, and a child under 18 who follows a faith is taken into its orphanage; see religion for what that can cost a house.
Your heir must be one of your own living children. You may name an unplayed child, change your choice or name nobody, from the child's own row under Account → House and family: each named child offers to be made heir, and the heir offers to be unnamed. If your named child is alive when you die, they take every title you held. Otherwise your eldest living child takes them. Twins are ordered consistently by their character record.
The children who did not receive the titles are dealt inheritance claims, one per title round-robin. A claim gives one attempt at that title under the same rules as a conquest claim; its source is shown as inheritance. If there is no living child, a duchy escheats to its king where one exists, and otherwise the title falls vacant.
The estate follows your account and the title follows the blood. Those paths can end at different characters: after your death you may take any available life, while another player may take your heir and play the person who holds your old titles.
A house that cannot produce an heir can take one in. Nothing here comes from the 2018 game, which had no adoption; it is built on the game's marriage handshake and the parents it recorded.
An offer is made from the other character's page, under Adoption, the way a proposal is: the page offers it or says which condition stops it. The character offered to answers from Account, where every offer made to them and by them stands with accept, decline and withdraw. It never accepts itself through silence, nobody else is asked, and it ends if either of you dies.
Who may offer. You must be alive, played and at least twenty. If you are married to somebody of the opposite sex, only the spouse whose house the children of your marriage join may adopt, since that is the house the adopted child joins too. Either spouse of a same-sex marriage may.
Whom. Anybody who is alive and played, younger than you, of another house, not your spouse, not your ancestor or your spouse's, and not already your child. Nothing else is asked of them: living parents, a marriage of their own, titles and an earlier adoption are no bar. A character nobody is playing cannot be offered adoption, because an offer needs somebody to answer it.
What accepting does. Their mother and father become you and, if you are
married to somebody of the opposite sex, your spouse. Otherwise you are their
one parent. The parents they had before are gone from their record; the
chronicle keeps what happened, and they gain the mark adopted, which every
reader can see and which changes nothing. They join your house, and every
descendant of theirs still in the house they left comes with them, the dead
included. A child of theirs who joined the other parent's house at birth stays
where they are, and so does their spouse. If they were the last living member
of their old house, that house is extinct and its name is free.
Afterwards they are your child for every purpose: you may name them heir, they are your eldest living child if they are, and they are dealt an inheritance claim with the rest when you die. Anybody who had named them heir before has named nobody now, and is told; a parent who is still their parent afterwards keeps the naming. Their old parents' succession forgets them.
An adoption cannot be undone. A house that regrets one has the remedy it has for any child, which is to name somebody else heir.