There are two types of list.
Your occupation and your wife's occupation should be in the same list.
Your occupation mechanical engineer is in MLTSSL list but your wife's occupation is depends upon her qualification and her particular field of experience. You did not mention here your wife's experience is in which field.
if it is in same list then your wife needs to achieve 6 band in each module score in IELTS and also needs to do skill assessment of her profile then you can claim her 5 points.