okay so what i think you/our teacher means by this is that Priam and Achilles both fixed in their roles of being the a king, 'a ceremonial figurehead that may just as well be of stone or wood', and Achilles being remembered as the 'most boldest, most ferocious and most unpredictable of the Greeks' as well as both knowing their fates; (Priam knows he is going to be 'shamelessly stripped and humiliated'. However, they do not want to be, particularly Priam, remembered by these images, and hence in taking a chance, Achilles 'breaks free from the obligation of always being the hero' as Priam 'is always expected to be a king'.
With the Hesione part, you talk about how Priam has had the 'foul slave smell that he cannot rub off' on him, where he has experienced where 'no matter how much we scrub ourselves' he can never forget. It is this experience that haunts Priam, and prompts him to carry out this moral act of heroism, because he knows that if he himself wasn't ransomed, he would have gone down that 'other path'. Because he knows it was a 'mockery intended' by the Gods, to 'show him what is was in their power to do', he feels affronted that he is to them an 'ancient doll', so in taking this chance, he breaks free from the restraints of the gods, and 'lets the real man inside' be brought forth.
Hope i helped