Change the login if you already have the appointment and paid them, these people are sh*t, they can try to extort more money by withholding your account.
Mention about friends and family, tell them you don't plan on meeting them because you are going to different city and you have to be back by XX for YY.
Qualifications: You specialise in ZZ and you have put yourself in a position where your work is valued and demonstrated your skills which are crucial for this ABC project.
Don't overthink it, you will most probably not even have to go through all of this with the work documents.