Yes!
Family, siblings, friends, etc are all allowed to play here from the same device or same location (IP address) as long as the following two simple rules are followed:
1. Each person Must have and use their own account (no account sharing)
2. All games played between people logging in from the same location Must be unrated games
For example, you and your brother are both in your room playing on Chess.com; you on the computer, and he on his phone. Since you are both connecting from the same location, you should only play unrated games together.