In the submission form (ITN) the coordinator has to declare that he/she has the consent of all applicants. How does the coordinator collect the consents?

In the form the quote reads: "The coordinator declares to have the explicit consent of all applicants on their participation and on the content of this proposal."
This means that the coordinator only has to declare that he/she received the consent from all applicants. It is up to the coordinator to collect the consents, for example via emails or letters.