The idea is simple. Mikey's two boys are coming of an age they will understand that their mother is not married to their father. This is shameful. Mikey has to marry her to expunge their sense of shame.
Unfortunately Mikey was married to Terri at the time, but Mikey couldn't just get a divorce from her since, after all, that, too was shameful!
A point of shame can be removed by eliminating the source of the shame. In the cultures that still use the "honor killing" that usually means killing the least powerful person in the conflict.
I note that Sicily was part of the Islamic world for several centuries. They may have been "Christianized" in a reconquest, but the "honor killing" tradition continues. It's really not surprising to see it resurface in Florida!
You do need to find your way back to reality some time in the near future.