The two of them were arguing so fiercely that no one dared step in.
Tips
grammar
Verb-object compound (劝 'urge' + 架 'fight') — like 离婚 'get divorced' or 见面 'meet', it splits: 劝了半天架 ('spent ages trying to break it up'), 劝过一次架. Don't try to put an object after it — the object is baked in.
