Obama kills family members all the time. what else would you call it when he drone strikes a wedding?
The US has a long standing policy of not deliberately targeting non-combatants. This is codified in both treaties and legislation. However, if a legitimate target, which can be person, place, or thing, is occupied by or adjacent to non-combatants, you can legally strike it.
Most civilian casualties over the past 15 years are from either striking a legitimate target when civilians are present (usually when there is no better option), or striking the wrong place due to an error. Hitting a wedding can be either.