WolfhoundJack wrote:
Interesting. I always go with 'Muintir' as my default because I tend to include some favorite cousins that live in other states/regions in my definition of "Family" and I was taught 'Teaghlach' was pretty much immediate family/nearby. Learn something new.

I think the choice can also be dialectical, or even just based on personal preference (in Scotland, for example,
muintir can sound a bit old fashioned in some contexts, and
teaghlach is much more common). Here's a summary of the basic idea, plumlily:
Not all speakers agree precisely on this, but in Irish,
teaghlach usually refers to the folks in your household;
muintir usually refers to a broader category of people (depending on the context, it can mean your whole family, beyond just the ones in your home, or even your tribe or your “people”), and
clann [from which we get the English word "clan"] may mean different things in context, but often just your children and other descendants, for example:
--
mo chlann = my children
--
mo chlann mhac = my sons
--
Tá beirt chlainne agam = I have two children
--
mo chlann clainne = my grandchildren
Clann can also be used to refer to a group, organization, or traditional clan:
--
Clanna Gael = Gaels [as a people]
--
Clann na nGael = a particular Gaelic organization
--
Clann 'IcDhòmhnaill = Clan MacDonald [in Scottish
Gàidhlig -- this usage is more common in Scotland in the modern context]