For your scenario, follow the below steps :
You can develop four separate infopath forms, preferably you can pick blank form template.
Publish these as content type or deploy to farm level.
Active these forms as separate four site collection level features.
Create a form library. From the form library setting, go to advanced settings, select allow content ...
A Form Library is a specialized type of Document Library. Just like the Document Library, you cannot just call items.add() or list.addItem(), because you have to upload a file into the library before you have a listItem you can add metadata to.
To upload a file, you would first need to have an IO Stream of some sort, either a FileStream if you are reading ...