Form Questions and Field Mapping

Would someone be able to help me understand Pardot's mapping with Salesforce custom fields. 

From what I have read, if a custom field in Salesforce is already in use it will not come up as a field to choose from in Pardot. Is this still true?

Our situation:

We have 3 forms on our website that ask about an animal. The 3 forms have different content around them, but ask the same questions. For example, what brand are you currently buying. I would like these 3 Pardot fields to be mapped to 1 field in Salesforce. Is this possible?