A SISTER and brother are suing their mother for negligence after their father fell 29 floors to his death. Ip Yuen-ha, 22, and Ip Chi-lun, 21, have issued a writ against Lee Yee-shun, 47, on behalf of their siblings and grandmother. If the action against Ms Lee and Ho Pong 280 Management Ltd is successful, Ms Lee, as one of her husband's dependants, will also benefit. The children's father, Ip Ching, 42, plunged to his death on August 8, 1991, as he erected scaffolding outside a property in the New Territories. Ip had worked for his wife's firm, Ngai Lik Scaffolding Factory, for 20 years, and earned $7,800 a month. He died after Ho Pong 280 Management asked the family firm to repair a building in Hong Lai Garden. Ip Yuen-ha and Ip Chi-lun are suing their mother and the management company for breach of contract and negligence. They claim the defendants failed to provide guard rails, safety nets and proper tools.