For multiple quotechars use regex in place of sep:
df = pd.read_csv(log_file,
sep=r'\s(?=(?:[^"]*"[^"]*")*[^"]*$)(?![^\[]*\])',
engine='python',
usecols=[0, 3, 4, 5, 6, 7, 8],
names=['ip', 'time', 'request', 'status', 'size', 'referer', 'user_agent'],
na_values='-',
header=None
)