A noble house is just a group of nobles who are related by birth, marriage or adoption - who work together for their common good. Any individual, no matter how influential or powerful are, will eventually die. If they are really lucky, they might finish up in the history books. However, you they establish a Noble House, it will (probably) endure - and then your name will live on as the Founder of that house. You will leave a legacy.
While some (often smaller) noble houses have a single established leader, the most powerful noble houses have many leaders and powerful people, often in different places – all working towards the same family goals. That doesn’t stop them having individual goals, or striving to increase their personal wealth/power/influence – it just means they bend their personal goals so that the ‘family’ benefit as well. There are benefits for the individual as well - if you take on one part of a Noble House, the rest of it is will probably come to their defence. Suddenly, you might find three, four or more ‘nobles’ arrayed against you. Some examples of powerful houses include:
Noble houses need to add people to their numbers just to survive. As the older generation pass away, the new generation, and their spouses, take over. Their children will form the next generation of the house. But sometimes that just isn't enough, and for those times there is adoption. There are three mains ways to add significant members to the House.
Naming Conventions This is written, primarily, from the perspective of a Patriarchal Society – partly because that is what I am used to and partly because my game settings are somewhat patriarchal. That doesn’t mean this is the only interpretation acceptable in my worlds, or that women can’t be head of a Major House. But most importantly - this isn’t a rule and it isn’t compulsory :} If you want something different for your character’s House – then go for it. This is just the default version I use when I am building a noble house, and even then it doesn't apply every time.
The House Name is normally only used by Heads of Family and their immediate descendants. For example Henry LeMaistre and Cyrus Ondari – along with all of their offspring take the House name as it is. Cyrus’s brother also has the name Ondari, and is heir to another branch of the house so his children would also take the house name as their own. This is normally restricted to people who are (or have been) children of the Head of Family. So this is to be restricted to Uncles, Aunts, Brother, Sisters and Children of the current head of family. That said, a Head of Family can adopt anyone as his/her Child, Brother, Sister or (more likely) cousin and confer on them the right to use the main family name.
The Nobiliary Particle is generally reserved for cousins of the Head of Family. It might be an adopted cousin or a cousin ten times removed - but all cousins may take the family name with a nobiliary particle. People adopted into the family or marrying in at ‘Cousin’ level normally take this as a family name. Some examples are: de LeMaistre, der lin Lebeda; de Lebeda (different branch of the family?), D’Lodkova, DoZimmer, d’Cordain. These are just examples - you could choose from Af, Der, Du, Von, Zu, or any of the examples on This wikipedia page - or anything else you think is suitable.
Double Barrelled Names imply a relationship with two families at once. Kao-LeMaistre and Lebeda-Ondari might represent married women (or husbands) of Heads of Family who still retain some loyalty to their previous family. It is often the sign of some sort of relationship between the two families. On the other hand ‘Mariam doZimmer Wolfeater’ is a single woman who is aligned both with the Zimmer and Wolfeater clans.
Most Noble Families insist that all of their contracts, including Family Incorporation, Marriages and Adoptions are overseen by a priest of Abadar and that a copy of all contracts are held in their archives. Other religions carry out marriages, but they are generally considered to fall outside the scope of Family Incorporation Contracts.
While most cousins, in game, will be PCs or independent NPCs - Entourage Cousins are a device to help expand the family, and bring in a few BP, using your entourage members - or by bringing in new members of your entourage. You can find the rules for them on the Entourage Page.