1. We set up a "Change Data Value" flow step after a form is submitted that changes the orignating web page attribute in the step. The new value becomes "http://{{trigger.web page}}". We then also send an alert to the lead owner which populates this field as a token.
2. You could create a new field for this Property ID, and then associate it as a hidden field on the form, populated to the corresponding ID, depdnding on which page the form resides.