Paul Lewis, 54, from Swansea is accused of handing over the cash to Dominique Saunders, 35, to arrange the murder of his ex-wife, Joanne Atkinson-Lewis.
A 43-year-old woman, a 15-year-old girl, and two boys - aged eight and four - all died at the scene in Tillett Close in Stonebridge, north west London, in the early hours of Saturday morning.
Special needs worker Wendy Lau threw stones, banged on the wall in the early hours of the morning and pointed a CCTV camera at Abigail Beckett's new house, a judge was told.