Ní ag dul ar an dtaobh eile don ndomhan atánn tú - It's not going to the other side of the world that you are.

Ná ní ag dul ar an dtaobh eile don ndomhan atánn tú: "Nor is it going to the other side of the world that you are."

I would have assumed that "Bob" refers to "Máire" since there seems to be too much distance between "deartháir" and "go dtugtaí Bob uirthi" for "Bob" to refer to "deartháir". (Maybe Máire was something of a pioneer. )

But the part I don't understand is this: "bhí deirfiúr dóibh Máire". Maybe there is a missing comma here and it should read "bhí deirfiúr dóibh, Máire". In that case, the whole thing would seem to say: "...a brother of Mam whom I knew well in London; and a sister of theirs, Máire, who was called Bob, was..."

It might be clearer if you gave the full sentence.

I don't think that would make sense in this context:

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

Is minic a chuala duine ag rá ag baile dá mbeadh éinne ag fágaint an tí go huaigneach ag dul go Sasana nó Meiriceá: 'Ná ní ag dul ar an dtaobh eile don ndomhan atánn tú!'

It makes perfect sense:
I often heard people say at home, if someone was leaving his home and going on his own to England or America, "well, it's not like you're going to the other side of the world!" (By contrast, the author ended up in Australia, and so did end up on the other side of the world.)

Thanks, that makes sense now. I guess I'm just not used to hearing such conjunctions at the beginning of sentences.

_________________
I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

234 - 236

ins gach aon áit prepositions can take their forms that appear before the article when preceding gach (i.e. ins as in insan), though Tomás Ó Criomhthain also had is gach aon áit where the preposition just took -s
éide 'clothing'
croiméal 'moustache'

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

croimeál: kro'mʹial (i.e with /o/ in the first syllable)

237 - 239

ambasáid 'embassy'
m'anam an diucs 'bless my soul'

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

m'anam an diucs 'bless my soul'

Are you sure this is the meaning? For a start it should be m'anam don diucs, or m'anam 'on diucs if the d is elided. It is not "an". Pádraig Ó Fiannachta really exposes himself in the editing of this word as a native speaker who understood less about Irish than he claimed.

Surely m'anam 'on diucs is Oh Christ! Damn! or something like that? Does that suit the context?

Diucs is a way of saying m'anam 'on diabhal without saying a sacrilegious thing.

I got the translation from here https://en.wiktionary.org/wiki/diucs, if it's at all reliable. It definitely should be spelt 'on, though an is the spelling used in the book. Was Pádraig Ó Fiannachta a native speaker? I hadn't known

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar