I've sent all my documents (about seven different times) to USCIS TSC by priority overnight USPS. Just in a regular postoffice, cheap and quick. Never had a problem ever.
I have sent my documents and my husbands in the same evelope. Just put the documents in different folders and have a separate package of documents for you and your wife, duplicate everything in your and her forlders. I use transparent plastic folders and put on top of all the documents (inside each folder) the application form with the stapled check and stapled envelope with pictures. Do not forget that the pictures should NOT be digital (see the forum) ! Good luck !
