Hello Charris,
When you use SharePoint Designer, one of the limitations is that you cannot use a workflow developed in SharePoint Designer on more than one library. If you need to use a workflow on more than one form library, you will need to develop the workflow in .NET.
If you want to have multiple workflows running in the library and have it based on the different forms you have in the library, you will need to publish the forms as a site content type and then add them as a content type to the document library you want to host them. For instance, if you want to have an Expense Report and an Asset Tracker form in one library, publish both as a content type, enable the management of content types in the library, and add both of your content types. This way, you will have both of your forms' fields to work with.