unexpectedly
The likely word is unfailing.
Aloof
loveless / unloved, or lonely
The word is cohabitation.
There is no one-word substitute in English for "son-in-law."
The adverb could be freely or voluntarily.
The word you want is florist.
Sportsmanship is a word substitute for spirit of game
The word metalworking is one word.
One possible substitute for "their" is "his" or "her" depending on the gender of the person/people being referred to. Another substitute can be "its" when referring to a non-human object or entity.
eat, use
The word that works is idiot.