The brothers, aged 29 and 33, are key figures in the McCarthy-Dundon criminal gang based in the south side of Limerick city.
The two men are due to face separate charges in relation to the incident.
A 21-year-old woman who is related to the men, was also arrested yesterday as part of the investigation.
The three were questioned at separate Garda stations in relation to alleged threats made against an ex-girlfriend of another family member.
They were also being quizzed about threats made against the woman’s father and brother.
The 23-year-old woman at the centre of the complaint is the former partner of a leading member of the McCarthy-Dundon gang and they have three children together. She has made a formal complaint to gardaí about the threats made against her.
The two brothers were arrested at 8.40pm on Monday as part of a planned operation involving members of the Armed Response Unit.
The men were arrested in the Hyde Road area of Limerick, the stronghold of the McCarthy-Dundon criminal outfit.
They were being held under Section Five of the Non Fatal Offences Against the Persons Act.
The 29-year-old was being detained at Henry Street Garda Station while the 33-year-old was in custody at Roxboro Garda Station.
The 21-year-old woman was also being questioned at Henry Street.
Two other men aged in their early 20s were also arrested yesterday as part of the same inquiry.
They were being detained at Bruff Garda Station in Co Limerick and at Mayorstone Garda Station in the city.