In cases like these, I would say "no way" since they're becoming step brothers. BUT, they were in a relationship before their parents so I honestly don't think it's fair for them to throw it away just cuz their parents decided to get married way after they started dating, you know? Even if the parents knew they were dating, they still might've developed feelings for each other anyways and still decided to get married. My point is, I don't really see anything wrong it, as long as they were in a relationship before things started happening with their parents.
In cases like these, I would say "no way" since they're becoming step brothers. BUT, they were in a relationship before their parents so I honestly don't think it's fair for them to throw it away just cuz their parents decided to get married way after they started dating, you know? Even if the parents knew they were dating, they still might've developed feelings for each other anyways and still decided to get married. My point is, I don't really see anything wrong it, as long as they were in a relationship before things started happening with their parents.