Two internal interfaces bridge with same dhcp and subnet

Question

Hi! 
 I have a Server 2016 Hyper-V host. 
 Right now Sophos UTM9 VM, has three virtual NICS. 
 1) WAN - External Hyper-V virtual switch, dedicated physical nic 
 2) LAN - Internal Hyper-V virtual switch 
 3) LAN2 - External Hyper-V virtual switch, dedicated physical nic 
 UTM works great with NIC1 and 2, i have internet and lan connection for all the virtual machines. 
 Now i am not sure, that i can do it, but this is why i started this question topic. 
 
 Can i get the NIC3, that is actually bounded to physical nic, to extend the same internal lan to external switch so i can extend my virtual network to other physical devices. 
 I tried to configure second nic, at sophos it is Internal interface as bridge with the additonal nic three. 
 All my virtual machines have internet and lan connection, but for the third nic, there is no connection at all.

Joosep1 · Answer

In interfaces Edit "Internal Network". Under "Type" Dropdown to Ethernet Bridge. Than "Bridge selected NICs" check the desired NIC's. And you should get a picture like the attachment. No further configuration is needed 
 
 As user oldeda wrote, i added the second, nic, edited the existing lan interface and changed it to bridge, also adding the second nic to the bridge and i got the same configuration as on the picture. 
 But, i forget, that missing key component for making it work with Hyper-V, i need to switch on "Enable mac address spoofing" for BOTH virtual lan network adapter, that are used in the bridge! 
 Also, Realtek NIC is junk, throw it away :) First i was able to get a connection for a test virtual machine with the second lan interface and additional Hyper-V virtual switch. 
 Configuring the second lan interface for a Hyper-V external network (selecting physical nic), at first, i could not get connection for physical netowork. 
 Changing from Realtek nic to a USB one and it works!!! My virtual UTM VM serves now both, virtual VMs and hyper-v host network plus all physical devices connected with a switch