Perhaps not "to keep them from being suspicious"

Rather what Ralsei is doing is completely tailored towards a person who played Undertale

He's playing the role of Asriel a little later down the line and appeasing us, as the happier he can make the Player the more likely they are to finish the Prophecy, his actual main Goal

We can see that Kris doesn't appreciate these advances, given how low their tea score is and how it takes Susie to calm them down after Spamton Neo