Luca and Grace - if that's Luca really being into a girl, he's got the romantic range of a rock...I've really seen a man acting so bored around a woman! Don't think Grace is buying it either, or cares to be honest...probably hoping someone more her speed will come in.
Regarding Ron and Scott...I think they are probably being heavily 'prompted' (told) by the producers to give up and leave. It makes what is a very boring series more interesting and gives them room to bring in more 'bombshells' quicker than if they just let it all play out naturally.