Chen Xin can ask Gao Sheng and Dong Zhang or any one of them to take full responsibility. Article 66 of the General Principles of the Civil Law stipulates that if an agent colludes with a third party and damages the interests of the principal, the agent and the third party shall bear joint liability.
If Chen Xin only entrusts Dong Zhang to take care of his house temporarily in this case, then Dong Zhang's behavior belongs to the legal act with no right to dispose of other people's property, and its effect is uncertain.
Chen Xin enjoys the right of ratification.
If Chen Xin refuses to let Dong Zhang sell the house, and Dong Zhang sells the house in the name of Chen Xin, it is beyond the power of attorney, and its effectiveness is to be determined, which requires Chen Xin's ratification.