The sunnah is to hasten to break your fast. You could choose some days to have iftar with your family and some days to have iftar in the mosque with the congregation.

Fasting is not invalidated in either case – whether showing the `awrah is done deliberately or by mistake.

When the sun has set, it becomes permissible for the fasting person to break the fast, whether the muadhdhin has given the adhan or not. What counts is the setting of the sun.