As China tries to control the narrative, the police in Wuhan, where the pandemic began, have been dispatched to break up groups on WeChat, a popular messaging app, set up by the relatives of coronavirus victims. Government censors have scrubbed images circulating on social media showing relatives in the city lining up at funeral homes to collect ashes. Officials have assigned minders to relatives like Mr. Liu, to follow them as they pick burial plots, claim their loved ones’ remains and bury them, grieving family members say.