Hey there, so to help with my learning I've decided in my spare time I'd attempt to write poetry as gaeilge , so I was wondering if someone could help me with this one line?

'Clann na gCibhleacháin go brách'

If I'm right, that's 'The Children of Cibhleacháin for ever'; but I'm not entirely sure whether I should be using clann or if I should be using clainne, because it's the children of someone it's possessive? So should it be the later genitive form?

And if it's not the genitive form do I remove the eclipse on Cibhleacháin?

Thank you

Clann Uí Chibhleacháin go brách/abú.

"na gCibhleachán" would be "of the Cibhleacháns", and normally "Ó" as in your surname is followed by the name of one person. Eg. Ó Conaill = the grandson/descendent of Conall.

_________________
Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Ah okay thank you, but Isn't Uí used to say 'wife of the descendant of xyz' would I not want to use Ua?

bean Uí = wife of the descendant. The word bean (= woman) is usually omitted, so:
Síle (bean) Uí Chibhleacháin = Síle (wife) of the descendant of Cibhleachán, anglicized perhaps Sheela O'Kevlihan

Clann Uí Chibhleacháin = the offspring of the descendant of Cibhleachán

Ua is just another version for Ó
Pól Ua Cibhleacháin = Pól Ó Cibhleacháin.

To clarify, "Uí" is the genitive for "Ó/Ua" so it's used whenever you have "X of Ó/Ua." In the case of "wife," it's literally "woman of Ó/Ua." It's not an exclusively feminine thing.

Redwolf

Go raibh maith agat! Learn something new every day!

Actually lads, "Clann Uí Chibhleacháin" means "Children of Ó Cibhleacháin/Children of a Descendant of Cibhleachán",.i. the ancestor was Ó Cibhleacháin, and not Cibhleachán himself.

"Clann Chibhleacháin" would be "The Children of Cibhleachán" (himself). (cf. Clanna Néill, Clann Dómhnaill srl.)

As a reference to a family, Muintir would be more correct. (Clann with surnames Ó Maol/Mac) So: "Muintir Chibhleacháin", the Keevlins.

Uí can be used there : clann Uí Dhomhnaill (the O'Donnell family), clann Uí Dhálaigh...

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

So, Clann Cibhleacháin would be 'Children of Cibhleacháin', but using Muintir would probably be more accurate if I'm referring to a family/community as a whole, which would be more like 'Family of Cibhleacháin'?

Yes.

BTW: Your ancestor's name is Cibhleachán. (suffix -án)
Cibhleacháin is the genitive form ("Cibhleachán's", "of Cibhleachán")