Need suggestions on how to properly segregate & load balance a network

I need some clarity on setting up a large network in my office. I have 3 businesses that share the same physical space and have several remote offices. There are also other business entities that fall under the umbrella of these 3 business which will need access to the same network.

Here is a visualization of what the environment will look like:

Company A — Company B — Company C
SubA1 — SubB1 — SubC1
SubA2 — SubB2 — SubC2
SubA3 — SubB3 — SubC3
SubA4 — SubB4 — SubC4

etc…