Six multi-component room-temperature ferroelectric liquid crystal mixtures are investigated using X-ray diffraction and polarization studies. Layer spacing and average intermolecular distance in SmC* phase are found to differ marginally. In two mixtures layer spacings show slightly increasing trend with temperature whereas in three other mixtures it shows slightly decreasing trend, in the remaining mixture it remains almost constant. Tilt angles determined from X-ray data are found to be similar to those observed from optical measurements. Spontaneous polarisations are found to vary widely and associated critical exponent is observed to deviate from the mean field value.