The posuk says Shimon and Levi took swords and killed all the male inhabitants : so why in the next posuk a) does it repeat that they killed Chamor and Schem and b) that they used swords ? Both these facts are already told to us in the previous posuk ??
It is telling us the sequence of events.
First they killed all the other inhabitants and only then were they able to find Shechem and Chamor to kill. ( Ohr HaChaim and possibly the Seforno).
This sequence is important to know because as The Ohr Hachaim says that if not for this sequence they never would have killed the inhabitants of Shechem to begin with. At first, they only wanted to Shechem and Chamor but the residents put up a fight to protect them so they had to be killed first to get Dinah out of there.
(Note : Other Rishonim give other reasons for why they killed the inhabitants and Yaakov disapproved of this mass killing)