If a contractor has filed a lien , do we as a subcontractor have to file as well to the owner?
You do not have to, but if you are not getting paid, it very well may be advisable for you to record a lien (assuming you have served a preliminary notice if you were required to do so) to secure your claim. For example, perhaps the contractor has not satisfied all of the prerequisites to assert a proper claim or perhaps the owner has other defenses against the contractor.