Keith Cowell, his son Matthew and a third man were shot dead
A drug dealer hid while his uncle, cousin and friend were gunned down, a court has heard.
Keith Cowell, 52, his son Matthew, 17, and Tony Dulieu, 33, from Essex, were "executed" at the Cowells' Bishop's Stortford house on 28 August, 2007.
Brothers Kevan Thakrar, 21, of Lomond Way, Stevenage, and Miran Thakrar, 24, of no fixed address, deny three counts of murder at St Albans Crown Court.
Ian Jennings said he was at the house to complete a drugs deal.
Mr Jennings, the nephew of Keith Cowell, told the court the £30,000 cocaine deal was with a man known as Mike.
'Shot the dog'
On 28 August 28, Mr Jennings agreed to meet Mike at the home of Keith and Matthew Cowell.
The three men were in the house, along with Mr Jennings' mother Christine Jennings, friend Tony Dulieu, Matthew Cowell's girlfriend Clare Evans and a three-year-old child.
Mr Jennings told the court: "I put the drugs on the dining room table, went into the kitchen to get myself a drink.
"I then heard a knock at the door, and someone come in. They pushed the door shut, they stood there, told everyone to get down on the floor.
"I saw the two Asian guys standing with a gun. They then shot the dog.
"At that point I ran. Inside the house all I could hear was gunshots, screaming, crying, glass breaking."
Kevan and Miran Thakrar also deny attempting to murder Mrs Jennings, 54, and Ms Evans, 23.
The Thakrars also deny possession of an Ingram Mac 10 sub-machine gun with intent.
The defendants' brother Jay Thakrar, 25, of Lomond Way, Stevenage, denies two counts of assisting an offender.
Their father, Atul Thakrar, 47, of Compton Place, Northwood, London, pleaded not guilty to assisting Kevan Thakrar to attempt to leave the UK between 28 August and 5 September.
Co-defendant Amanda Dansie, 21, of High Street, Buntingford, Hertfordshire, pleaded not guilty to assisting in the escape of Miran Thakrar from the UK between 28 August and 9 September.
Yilay Tufensoy, 20, of Nags Head Road, Enfield, London, denies two charges of assisting an offender.
The trial continues.