Could it be that Seth found out Isis has cursed him not to have a family when he asked her to be his queen, so he decided to kill her in order to remove the curse?
It somehow can explain why he killed those who looked like her
Not unless Seth was lying in chapter 39, when he said he had a completely different reason for killing the women that ressembled her (but that was proven true when it turned out his cursed weapon had indeed been made of the soul of innocent people he had murdered, including those women). Moreover, no one ever mentioned even the mere belief that the curse could be lifted if Isis dies... As for what Seth knew, he only knew about the curse that "neither he nor Isis would get what they want" because Isis had told him that to his very face the very moment she tearfully rejected his advances, before he imprisoned and she escaped. But he didn't know about the part where the curse allegedly affected his relationship with his family.
Did Jin accidentally break Matthew's glasses?
Yes, he stepped on them accidentally.
I was hoping he would have done it on purpose just to be able to look at those perfect eyes directly. ٩(๑❛ᴗ❛๑)۶
But that's OK.