Hello Dion, Welcome to the Q&A forums. It could be beneficial to know more details of your situation like OS and such.
The general answer is that only one local login is allowed, and one through RDP. Any additional login results in disconnecting the older active session. Things get complicated when you add other types of connections, such as file-sharing connections or Administrator accounts.
If you use RDP, the limit of all concurrent "connections" is typically 20, but for full user login it's only 1, as described above.
In theory you could both be Administrators, allowing for both of you to connect to the VM, or just one user and one Admin. If you need multiple concurrent user sessions in the same VM, you will need a Windows Server OS and use Remote Desktop Services to create a remote desktop session pool. It does require some prior reading to understand how to deploy it, but all documentation is publicly available.