Multiple Networks

Hey everyone! I am having a few issues trying to setup multiple virtual networks. The end goal is to have 3 separate networks, where Network B can see Network A & Network C, but Network A cannot see Network C.
I have tried putting these on the same virtual bridge and use Security Groups to restrict traffic, but traffic flows across all 3 networks regardless.
I have also tried creating multiple interfaces so each network has their own, but then the networks cannot see each other at all.
I have also tried using the virtual router but I’m not sure where to put the rules to drop certain traffic that comes through it.

Virtualization in general is new to me and any advice that would point me in the general direction to configure this correctly would be appreciated!