Triple net is where the tenant not only pays rent, but also pays for maintenance and taxes on the property.
Furnace breaks? Roof leaks? Pipes freeze?
Are all the tenant's problem, not the landlords.
Property taxes increase? Tenant's problem. At least until the tenant moves out, then it becomes the landlords problem until they can find another tenant.
These are generally true of a triple net lease, but can be negotiated to just about any arrangement in a commercial lease.
Sure, but sometimes both entities have the same owner and are separated for liability purposes.
It all depends on the two (or more) business entities and what they are willing to negotiate.