Can we pray for non muslims who are in need?
– What if they were first muslims then converted to another religion, can we still pray for them?
– What if they are your blood relative but not muslims?

Can we mention their names in special namaz or duas ie: namaze shab, namaze jafare tayyar or in dua e samat etc?

Yes you can pray and add one important dua also that oh Allah guide them right path also.