Can a girl have a sexual relationship with two brothers?

Good afternoon Aunty Amara. I have a question that has been bothering me because the lady in question is my friend. 
Can a girl have a sexual relationship with two brothers? 
She dated one in the past and is presently dating the older brother. 
She claims she hates the younger one with a passion and doesn't want to have anything to do with the younger one again. 
Which makes me really confused as to why she was now dating the older brother. 
Please we need a feedback as soon as possible before everyone involved gets hurt.

Dear sender,
At the face value it doesn't look harmful but I worry personally why a lady would decide to date the elder brother of her ex.
What then would be her dignity as a lady and assuming that sex was part of the menu, how comfortable would she feel sharing her meal to another brother of the same mum.
I feel it's an obsession with the family that may have made her decide to date his brother either to get back at him or get into the family by any means.
I hope it works out for them but I am still afraid they may simply use her and give her the exeat once they're done with her services.
But then again, it's her life and her choice so if she's comfortable with it, what else would you do than hope that it works in her favour.