No, there is no harem.
There are branching options. One is love with the girlfriend, one is family but even the family one has you pick between mother or sister.
There is no way to get them together.
There is an option in the girlfriend path to let her friend watch which looks like it might slowly let her join in or let her friend bang one of his friends.
The closest to a harem is maybe a 3way with the girlfriend and her friend but even then it may only be a few scenes.
The other options are NTR ones.