Need some advice to deal with teenage boys

[aussie]

OK i have bit of a problem to deal with today and was hoping some of you guys would give me some advice.

PLEASE NO JOKES OR BEING STUPID

my to oldest boys got in to a punch on over a friend who was staying over the weekend . the problem is one got stabbed with siscors by the other and needed 4 stiches
the problem is both have completely different stories and dont no what to belive

all i can say when i ran in the room the oldest was chooking out the youger one and i ripped them appart

now my wife said i have to deal with it . when i ask what happen i get alot of yelling.

one off my thoughts was to go to the cops and let them deal with it . he cant go around stabbing people and especally his bro. dont want to push this problem under the mat any advice would be good