Assuming host eth0 interface of 192.168.0.10 / 255.255.255.0 gateway 192.168.0.1
# configure nic1 on each VM to be bridged to the host's main interface (eth0)
VBoxManage modifyvm VM1 --nic1 bridged --bridgeadapter1 eth0
VBoxManage modifyvm VM2 --nic1 bridged --bridgeadapter1 eth0
VBoxManage modifyvm VM3 --nic1 bridged --bridgeadapter1 eth0
VBoxManage modifyvm VM4 --nic1 bridged --bridgeadapter1 eth0

# list known bridged interfaces
VBoxManage list bridgedifs

Now go into each guest and configure their networking directly (not using VBoxManage)
e.g. use Windows control panel to configure your guests
VM1 192.168.0.11 / 255.255.255.0 gateway 192.168.0.1
VM2 192.168.0.12 / 255.255.255.0 gateway 192.168.0.1
VM3 192.168.0.13 / 255.255.255.0 gateway 192.168.0.1
VM4 192.168.0.12 / 255.255.255.0 gateway 192.168.0.1

If you want the guests to communicate with the host then they must be on the same subnet at the host.