That MIL house is only slightly over 400 sq ft TOTAL. I do not know what year the “cottage” was built, but the interior sq footage is very cramped. Such structures are often built for the widowed in-law to live in. The cottage should have it’s own postal address if used as a rental.
http://www.freerepublic.com/focus/chat/2897205/posts?page=78#78
found an old entry that describes the property as it was...there was no rentable outbuilding there. Love your research, PSST...Wanna See my Polk? LOL!