One option is to change the network adaptor of the virtual machine to bridged mode; you should then be able to access the virtual server from the other machines on the network, by providing your guest's IP address.
For practical aspects, look at the VirtualBox documentation on Virtual networking. Your options are to use bridged networking
With bridged networking, VirtualBox uses a device driver on your host
system that filters data from your physical network adapter. This
driver is therefore called a "net filter" driver. This allows
VirtualBox to intercept data from the physical network and inject data
into it, effectively creating a new network interface in software.
When a guest is using such a new software interface, it looks to the
host system as though the guest were physically connected to the
interface using a network cable: the host can send data to the guest
through that interface and receive data from it. This means that you
can set up routing or bridging between the guest and the rest of your
or port forwarding:
As the virtual machine is connected to a private network internal to
VirtualBox and invisible to the host, network services on the guest
are not accessible to the host machine or to other computers on the
same network. However, like a physical router, VirtualBox can make
selected services available to the world outside the guest through
port forwarding. This means that VirtualBox listens to certain ports
on the host and resends all packets which arrive there to the guest,
on the same or a different port.
So, in case of a NAT port forwarding, you should use the following command:
VBoxManage modifyvm "VM name" --natpf1 "guesthttp,tcp,,80,,80"