So finally I adapted one filter to get the zerofrequency and another bandpassfilter to get the 600 Hz frequency. Passzero has to be true just for the zerofrequency then it works. I'm not yet happy with the phase delay but I'm working on it.
1)bandpass 600 Hz:
taps_bp = bandpass_fir(ntaps, lowcut, highcut, fs)
Function for the bandpassfilter
def bp_fir(ntaps, lowcut, highcut, fs, window = 'hamming')
taps = scipy.signal.firwin(ntaps,[lowcut, highcut],nyq, pass_zero=False)
return taps
2)zerofrequency filter
taps_zerofrequency = zero_fir(ntaps, zerofreq=1, fs)
Function for the zerofrequency filter
def zero_fir(ntaps, zerofreq, fs, window = 'hamming')
taps = scipy.signal.firwin(ntaps,[zerofreq],nyq, pass_zero=True)
return taps