Three people were in police custody last night in connection with the weekend murders of Richard, Mark and Jason Quinn in an arson attack on the children's home in Ballymoney, Co Antrim.
Two men, believed to come from the Ballymoney area, were arrested by police yesterday for questioning about the attack, which the RUC insists was sectarian.
A man arrested earlier this week remains in custody, while another man was released on Wednesday without charge.
Orangemen in Portadown, meanwhile, are planning to step up their protest with a mass demonstration in the centre of the town tonight. The spokesman for Portadown district lodge, Mr David Jones, said the protest would prove that support for the Portadown Orangemen had not dwindled as the media suggested.
He said: "We are calling for a full turnout of people to come to Portadown to show they are still supporting us."
Mr Jones said tonight's protest would be followed by other actions across the North, as the situation was "developing into a battle of people-power for cultural and civil rights".
In Drumcree yesterday evening, the only Orangemen remaining in the field were the Portadown district master, Mr Harold Gracey, and 10 other district officers. A security operation, which lasted most of the day, was continuing and police were stopping other Orangemen from entering the area as a search for blast bombs continued.
Mr Jones said Mr Gracey and the others would stay in the field because they feared that if they left, the RUC would not allow them to re-enter.
The stand-off has now been going on for 11 days, and numbers have decreased dramatically since the murders of the three Quinn children last weekend.
The RUC searched the field throughout the day and three blast bombs were discovered at lunchtime.
A British army bomb disposal team was called in to defuse the devices. Another suspicious object was found later in the day, and army technical experts were still examining them last night.
Orangemen claimed the RUC was deliberately dragging out the security operation, but a police spokesman said they could not allow people to enter the area while there was a threat to life. "How can we let Orangemen in when they could stand on a blast bomb," he added.
Police said Orangemen would be allowed back when the area was judged safe.
Soldiers also strengthened the barricade across the Drumcree road and defences around the field yesterday, erecting more concrete bollards and barbed wire.
Mr Jones said that if the security operation was over by tonight, large numbers could return to the field from the protest in the centre of Portadown due to start at 7.30 p.m.
A "presence" would be maintained in the field despite the security operation, he said.
Meanwhile, a leading loyalist campaigner, Ms Pauline Gilmore, who was arrested in Drumcree on Wednesday, remained in police custody yesterday. She was being questioned in Castlereagh Holding Centre.