Based on the facts you have provided, the landlord is probably responsible. Best to consult with a lawyer.

We were served an eviction notice for the month of October, I paid it along with the fees, they want more...

If you paid all that was due for October, they have to serve a new five day notice to start proceedings for November.

Legal rights

Based on what you have told us, he remains liable on the lease whether he lives there or not. He cannot force you to take on new roommate. But...

Do I have to wait to be evicted before I can begin the legal process?

It is going to be hard to evict you if you've paid the rent, but take the lease to a lawyer for review.

How do I make this legal?

If the agreement was oral, you are in trouble. Get to a lawyer. There are a number of potential issues.

How would I defend this case?

With some exceptions, allegations are sufficient at the complaint stage. Later, the plaintiff will have to prove those allegations. See a lawyer.

During discovery period can a motion of summary judgement be granted? A court date is 90 days out, plaintiff files for SOJ i.e

Yes, although you might get the judge to postpone consideration of the motion if you need the rest of discovery to be able to respond.

I'm representing myself in Small Claims Court. Can I contact the other party for resolution without "going-thru" their attorney?

Should not be a problem since attorneys are not allowed in small claims.

Selected as the best answer

The tenant in your situation had a right to assume that the son, who the landlord had put out as her agent, was agent for all purposes unless the...

Is my lease still valid without my signature (I am the tenant) on it?

There are too many issues here to address them all in this form. Go see a lawyer.