I have her set as mc mother, in my playthrough she said ''i am your mo...", should be obvious she was going to say "i am your mom/mother".
And about Marcello thing, it made me wonder why would he all of a sudden think about mc and his mom in such a way, mc was quite surprised too. Now, after Claudia let mc have her so easy(and Claudia is anything but easy, i mean even though men hiting on her all the time and her hussbend is trash, she never even considered to cheat on him or just dump him), seems like she has been hiding forbidden feelings for mc, and Marcello knows about it or at least suspects, thats why he feels so insecure.