Conflict 1: If your friend hasn't locked it down yet and she's not his ex then that's fair game.
Conflict 2: Depends how much you value the friendship of her brother. Is he a mate from ages ago as in he's a good friend and you guys go way back, or you used to be friends a long time ago and don't really keep in contact.
- If you're still good friends with him I'd say bring it up with him first or just go for it and be prepared to cut that friendship.
- If you used to be friends butdon't keep in touch then there's no issue here, go smash.
And update the thread with how it goes. :o