Is it possible to have 2 leases for the same unit? Here's the scenario.

Lease 1

Tenant A signs a lease and Mom and Dad also sign.

This is a 1 year lease.

.

Lease 2

Tenant B (new fried of Tenant A) signs a separate lease agreement for the same property with the same lease expiration term as Lease 1. Tenant B passed the screening and would qualify individually.

Is it OK to have 2 "separate" leases for the same unit?

Legally, I'd say this is creating a mess. For example, I assume that since Mom and Dad are also signed onto the lease they are financially responsible for any damages to the property since they "co-signed" for Tenant A. That means they have rights, possibly rights to exclude folks not on the lease from being residents.

But if Tenant B also has a lease, do his rights run concurrent to, supersede, or are they "subject to" the original lease with Tenant A and his parents?

I know folks make up stuff like this all the time, and in most cases it probably doesn't cause any major problems. Where is DOES cause problems is if Tenant B does something dumb like set your house on fire. Parents of Tenant A may say they are not responsible because the land lord unilaterally modified the contract without their written consent and allowed someone else whom they did not approve of to have rights to the property.

Sorry, I didn't clarify enough.

Tenant A moved in October, 2017. Lease term 10/17-9/18

I would use a short lease addendum that both old and new renters sign. It would include their being jointly and severally liable and indicate how the security deposit is being paid and how it will be handled at the end.