Partner declaration forms can be exported/downloaded from the export section of JEMS, but ONLY AFTER THE SUBMISSION OF THE APPLICATION. Does this mean that partner declaration forms, including lead partner declaration forms can be submitted after the deadline for the submission of project applications? Also, can you confirm that deminimis declaration forms need to be submitted as well? If this is the case, where can I find the template of the forms, can the forms be downloaded before the submition of the application form and what is the deadline for submitting them?

Indeed, the Partner declarations can only be generated after the submission of your application, and need to be provided normally within 10 working days. In any case, the deadline is indicated in the ToR. Same applies to De Minimis (only for concerned partners).