The pair appeared at Letterkenny District Court yesterday after gardaí raided an apartment complex in the town on Sunday.
Detectives revealed the arrests of the four people at 1 Riverside Apartments, Pearse Rd, Letterkenny, were a culmination of a week-long undercover investigation.
Detective Sgt Michael Galvin told the court how all four, who are from Romania, admitted knowing prostitution was taking place in the apartment.
He told the court how gardaí seized numerous mobile phones, laptops, as well as €1,470 in cash which was the proceeds of prostitution.
Detective Galvin said that, while in the apartment, the various phones were ringing regularly and that one prospective client arrived.
He added that several items found in the apartment suggested that an active brothel was operating from the premises.
He said the women had advertised their services on the well-known contacts website, Escort Ireland.
Before the court were Mihia Margarit, aged 37, his sister Giorgiana Chiscon, aged 34, Adriane Niculu, aged 38, and Elena Florea, aged 35.
The court was told that the women were not being trafficked but we working for themselves and were sending the money back to relatives at home.
One of the women had three children and another was using the money she earned to put her 20-year-old son through college.
Another of the women was sending money back to her own country so a relative could have a serious medical operation in Spain.
Evidence was given that the average wage in Romania was €500 a month compared to the €50 to €60 the women were charging clients for sex for each half hour here.
The court was told that Mr Margarit had only arrived in Ireland recently and was only here to make sure his sister sent the money back to Romania as she had a serious gambling problem and was spending all her money in local casinos.
There was no evidence to suggest that Mr Margarit was putting undue pressure on any of the women to take part in prostitution.
Judge Paul Kelly asked Sgt Galvin if there was any evidence that the landlord knew what was happening in the premises and he was told there was no evidence.
The women were paying €120 each week to rent the apartment, which was an average rent in the area.
Judge Kelly ordered the destruction of the mobile phones and laptops and also ordered the seized cash of €1,470, be given to the State.
He also applied the Probation Act to all four defendants.