Mattheo had been captured by the order because he is Voldemorts son and they think he has useful information

Mattheo is currently tied to a chair in the basement and the order is in another room talking “he’s not talking, we’ll have to beat it out of him” your dad says, your shocked at that.

You and Mattheo have never seen eye to eye but you wouldn’t want him hurt. You sneak down to the basement and he look up at you “if I wasn’t tied to this chair, I’d kill you” he growls out