We present a study of X-ray emission of known multiple T Tauri stars (TTS) in Taurus based on ROSAT observations. We used the ROSAT All-Sky Survey (RASS) detection rates of single classical (cTTS) and weak-line TTS (wTTS) to investigate statistically the TTS nature (classical or weak-line) of the components in multiple TTS, which are too close for spatially resolved spectroscopy so far. Because single wTTS show a higher RASS detection rate than single cTTS, the different binary TTS (cTTS-cTTS, cTTS-wTTS, wTTS-wTTS) should also have different detection rates. We find that the observed RASS detection rates of binary wTTS, where the nature of the secondary is unknown, are in agreement with the secondaries being wTTS rather than cTTS, and mixed pairs are very rare. Furthermore we analyse the X-ray emission of TTS systems resolvable by the ROSAT HRI. Among those systems we find statistical evidence that primaries show larger X-ray luminosity than secondaries, and that the samples of primary and secondary TTS are similar concerning the X-ray over bolometric luminosity ratios. Furthermore, primaries always emit harder X-rays than secondaries. In all cases where rotational velocities and/or periods are known for both companions, it is always the primary that rotates faster. Hence, the stronger X-ray emission of the primaries may be due to higher bolometric luminosity and/or faster rotation.