A mortgage foreclosure civil action suit has been filed on a property that my deceased father owned. my siblings and I are being sued for his mortgage debt. I have to file a written response. Is it a matter of me writing a letter saying that I lay no claim to the property?

You need to do two things.  First, you will want to record a disclaimer in the public records of the county where the property is located.  A disclaimer is required to be in a certain form that is set forth by the Florida statutes, witnessed by two people and notarized.  Additionally, you will need to file a response, which is known as an answer.  In the answer, you will need to admit or deny the allegations of each paragraph in the Complaint.  You may also have affirmative defenses that you should assert.  I recommend that you contact an attorney to assist you in preparing the disclaimer and your answer.