Pursuant to divorce decree in the County of Richmond, State of New York, husband upon sale of his current residence is to pay wife sum of $50,000. Wife at her own cost and expense may record a mortgage against this property in said amount which shall bear no interest and shall contain no acceleration; or foreclosure provisions and shall be satisfied only upon sale of the property.

What forms do I need to file a mortgage/lien on the property and are there any websites that have it free with instructions for filing?

Go to the Richmond County (Staten Island) clerk's office. They will tell you what forms you need. You may be able to find them online if the clerk has a web site.