Complex sentence: Sullivan swears his son's secrecy but Connor acts on his own, sending Sullivan to a speakeasy to have him killed while murdering Sullivan's wife Annie and younger son Peter, mistaking him for young Michael.
Split into simpler sentences: Sullivan swears his son to secrecy but Connor acts on his own initiative. He sends Sullivan to a speakeasy where he has planned his death while murdering Sullivan's wife Annie and younger son Peter, mistaking him for the young Michael.