What should be written on the invitation letter? Do the invitee need to send her passport?

Which type does the invitee want to apply?
If it is just for L type, the passport of inviter is not necessry. The invitee's basic information (name, gender, etc), the invitee's visiting purpose and the inviter's basic information (name, contact telephone number, address, official stamp, etc).

If for other type, the inviter's passport may be needed.