Unable to RDP onto a VM hosted on another LAN computer

Solution 1:

use Bridge mode in the network adapters

from Virtual Box Networking Modes *Bridged Adapter

Under the Bridged Adapter, your virtual machines behave as any other computer on the network where the hosting system resides; it bridges the virtual and physical networks. The outside world can directly communicate with the guest machine.*

Using Bridged mode allows the guest OS to connect directly to the network. therefore the guest OS gets a different IP address independent to the Host OS.

Connection via RDP using the IP address of the Guest OS.

p/s: using port forwarding may also work. haven't used it though