If they have shown you a written ijazah of them being able to receive khums from the Marja', or you are of the level of trusting the individual in what they are saying about their receipt and its authority, then that would suffice.
If not, request a receipt from the office.
The requirement of A.U. Seyid Sistani's office is that whenever you give a khums payment, a receipt must be issued from the office.
It is permissible to place something solid in one's mouth while fasting, for the purpose of cooling down, or naturally creating saliva, as long as it is not swallowed, or taken out and placed back in mouth again.
An example for this is putting a coin in your mouth.
The emphasis is that the kafan be of one piece of cloth, and if needed to be sewn, then its own strings should be used. Furthermore, A.U. Seyid Sistani does not completely agree that it is makruh. Please see link.
Full Name and Password are required.
Please provide a valid Email address.
Please enter a valid email address.
Enter valid first name and last name with at least one space.
Mail sent successfully!
A validation e-mail has been sent to your e-mail address. You will need to follow the instructions in that message in order to gain full access to the site.