How would you say "My brother walks with me" in Irish?

One way would be Siúlann mo dheartháir liom.


Explanation:

The verb "to walk" is siúil. "He walks" is siúlann sé (verb first, pronoun second in Irish).

"Brother" is deartháir if the person is your real brother, bráthair if the person is an unrelated person you feel affiliated with.

"My" is mo which causes lenition (séimhiú) so "my brother" is mo dheartháir.

Prepositions and pronouns get joined together in Irish so "with me" is liom (= le + mé).

There might be other ways to express the sentiment ...

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Another possible option:

Siúleann mo dheartháir in éineacht liom

Not sure of the distinction, but I think "in éineacht" acts as something of an intensifier, emphasizing the "togetherness" of the situation. Open to correction on that, though.

Redwolf

Also "... le no thaobh". Might be read as "... by me"

Wouldn't that be - le mo thaobh ? (and do I get an extra point for pointing it out? )

Yep:

in éineacht liom means "with me" as in "together with me", "along with me", "simultaneously with me"

le mo thaobh means "with me" as in "beside me".

These are nice too - perhaps more poetic - but I think liom is also probably sufficient on its own. After all, the song Thíos Cois na Trá domh simply has "... na daoine a shiúladh liom thíos cois na trá" "the people who used to walk with me down by the shore".

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Yep, I agree