In the past, I had wondered how to say something like 'John and Mary O'Connell' in Irish if the two people concerned were married. Maybe, you could say 'Seán Ó Conaill agus Máire Uí Chonaill', but this seems a bit long-winded.

Anyway, I just stumbled on the webpage of a brother-sister musical duo from Co. Galway. They are named Séamus & Caoimhe Uí Fhlatharta. The surname format here is interesting. I wonder if it would work the same way for a married couple, for two brothers, father and son, mother and daughter, etc.?

Yes, that's how it's done for married people too.
I think usually the woman's name comes first, so that the surname is in the masculine version.
Máire agus Seán Ó Flatharta

I think I understand the rationale in saying 'Seán agus Máire Uí Chonaill' in the case of a brother and sister. The inclusion of brackets as follows would show the grammatical relationship between the words:

{Seán agus Máire} Uí Chonaill

In other words, it means {Seán agus Máire} of Ó Conaill, where the Ó Conaill man in question can be seen as either their father or some indeterminate patrilineal ancestor.

Presumably, for two brothers, it would be the same e.g. 'Seán agus Séamas Uí Chonaill', rather than 'Seán agus Séamas Ó Conaill', since 'Ó' is singular.

And presumably, for two sisters, it would work the same too e.g. 'Máire agus Úna Uí Chonaill', rather than 'Máire agus Úna Ní Chonaill', since 'Ní' is singular., being a contraction of 'Iníon Uí'.

And I'm guessing it would also work this way (i.e use of Uí) for other family relationships e.g. father and son, father and daughter, mother and son, mother and daugher; and even if you reversed the order e.g. son and father, daughter and father, son and mother, daughter and mother.

And it can also work this way for husband and wife, as you say. But, you point out,it is more usual to say 'Máire agus Seán Ó Flatharta' (with wife's name first). I suppose this can be rationalised by showing the following grammatical relationship between the words: {Máire} agus {Seán Ó Flatharta}.

I'm not an expert on surnames, and certainly not on genitives.


But for me "Uí" used in a surname is for married women.
Unless it's obviously plural like Clann Uí Fhlatharta, or Muintir Uí Fhlatharta, or placenames like Poill Uí Mhuireann.

So I'd use Ní for sisters who share the same surname.
I think "Ní" can also be short for both íníon and íníoneachaí.
Máire agus Bríd Ní Fhlatharta.

Same with brothers, Seán agus Páraic Ó Flatharta.
Because what you're saying is that they both have the same surname.
If talking about something both of them possessed then use "Uí". Like Siopa Sheáin agus Pháraic Uí Fhlatharta.

Now that may not be grammatically correct by the standard though. I don't know.

It is a modern thing for a Máire Ní Laeire who marries Seán Ó Briain to want to be known as Máire Uí Bhriain. This is because in English she adopts the husband's surname. But in Irish she is stil Máire Ní Laeire. Máire Uí Bhriain effectively means: Máire, Bean Uí Bhriain. She is the wife of Mr O'Brien, but she herself will always be a member of Muíntir Uí Laeire. That's looking at it traditionally. Of course, the influence of English and English cultural norms is a fact that Irish is adapting to.

In strong Gaeltacht areas people still use patronymic names. And everybody's name is unique. Surnames are secondary in the community, but must be used on anything official.

Curiously, where I come from (an English-speaking part of Kerry), there is a similar practice, so I'm guessing it's a remnant of when the area was Irish-speaking. If you have families of the same surname living in close proximity, children of each family might be known by their father's first name, which acts as an unofficial surname in order to distinguish the different families. Typically, the names will be English language names, there will no initial lenition of the father's name, and, if the father has an Irish language name, the genitive case form will not be used. E.g. Joe Billy (implying Joe, whose father is Billy), Kate Billy (Kate, whose father is Billy).

If, for whatever reason, the mother is more well-known in the locality (eg. if the father died young), they might instead be known by their mother's name e.g. Joe Mary.

Less often, the naming can go back two generations e.g. Joe Billy Pat (Billy, being the father, Pat the grandfather).

In practice, it's only a small few people who are known by this naming scheme, and typically these people would have very common surnames e.g O'Sullivan, McCarthy.

I wonder if 'An tUasal' for 'Mr.' is also a modern invention, again in imitation of the English language.

Societies can be described by various characteristics, one being degree of formality. For instance, Japanese culture is often described as being very formal by comparision to Europe. I get the feeling that Irish society was traditionally very informal, and so honorifics like Mr. and Mrs. might not have existed. For instance, the Irish language never developed a formal second-person singular pronoun, like is found in many (most?) European languages (including English, although the distinction between informal and formal subsequently died out in English).

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The following translations are given in De Bhaldraithe's dictionary:

Mister: Mr. Kyne, an Cadhnach, Mac Uí Chadhain; [Curiously, there is no mention of the construct 'An tUasal'.]
Miss: Miss Ward, Iníon Mhic an Bhaird.
Mrs. (under Mistress): Mrs. Sullivan, Bean Uí Shúilleabháin.

He doesn't give any way to say something like 'Mr. & Mrs. Murphy', although Google Translate gives 'An tUasal agus Bean Uí Mhurchú'.

"Mr and Mrs" is an English concept from the modern nuclear family and doesn't reflect traditional Irish culture. As you say, "an tUasal" was made up in the modern era to correspond to "Mr", but if you had to say "Mr and Mrs", you could translate it as you suggest.

Obviously, there are a certain number of modern usages that should be regarded as the natural development of the language.