How do historians decide what counts as ‘truth’ when sources conflict?

Question about Muhammad Ali Jinnah’s early life and family background?

Modern lockpickers can easily defeat advanced locks using very simple tools. Since historical locks were less sophisticated, was lockpicking a widespread problem in the past? Did people actually trust locks to secure their property?

The United Democratic Front (UDF) and Inkatha were both opposed to Apartheid in South Africa. What was the major source of conflict/ideological difference between the two parties that led to events such as the violence at the University of Zululand in 1983?

Why was there a 2000 year gap between the first city states and the first empire?

Why did the peaceful protest fail at Tiananmen Square? And why did the CCP act so violently towards the peaceful protesters?

Why do so many state-level governments in the US have bicameral legislatures?