I can give you many more evidences in regarding to Undertaker making RealCiel a doll but that'll take long so I'm just gonna point out that in the Arc where Undertaker turned out to be the principal, he said to FakeCiel that "This is my most successful creation of my dolls, Well. For now"
Undertaker gives “Ciel” something to drink, tells him not to wake up, pages 21-23:
http://www.mangago.me/read-manga/kuroshitsuji/an/v18/c108/pg-1/
Undertaker says “the ‘Earl of Phantomhive’ is still with us”, page 25:
http://www.mangago.me/read-manga/kuroshitsuji/an/v20/c105/pg-1/
“Ciel’s” Flashback nightmare with his twin, pages 13-19:
http://www.mangago.me/read-manga/kuroshitsuji/an/v18/c090/1.html/pg-1/
“Ciel’s” twin saying that Ciel sacrificed him during the ritual:
http://www.mangago.me/read-manga/kuroshitsuji/an/v18/c095/pg-1/
Undertaker talking about his masterpiece, pages 13-14:
http://www.mangago.me/read-manga/kuroshitsuji/an/kuroshitsuji-chapter-84.html/1/
Btw, there's a page where Ciel wakes up in the middle of the night and Undertaker says something like "it's too early wake up" then our Ciel open his eyes like it were a dream. I'd like to reread that chapter, does anyone know what is it?