Question for the MT Landlord/Tenant experts

I've got a question for you MT gurus about how to deal with an unruly landlord.

First let me frame the situation:

The house is an older 4 bedroom house. 3 bedrooms upstairs, and a finished basement with 1 bedroom downstairs. The downstairs bedroom does not have a window so it is not officially on the lease.

4 of us have been living here for close to a year, but only 3 people are on the lease. We had a verbal agreement with our landlord when we moved in that it was fine if we wanted to have a 4th person in the downstairs bedroom to make it cheaper for all of us.

Throughout the term of the lease we have had only one significant issue with the house, the septic tank failed and it took us about 5 months to get him to replace it. After he got it replaced the entire backyard is basically mud and he has refused to sod it/put straw down despite multiple complaints from neighbors/the city. This whole saga has been annoying and the backyard smell was awful, but it wasn't the end of the world or anything.

So now the landlord informs us that he is interested in selling the house, which is fine because our lease is up on 5/25. He flies into Atlanta (he lives in California) to check out the house. I met with him on Friday and he is very friendly, points out a few things such as there are a couple cigarette butts, broken mirror vanity in the bathroom, and there is a hole in one of the basement walls that I pointed out to him and said we could pay to fix it ourselves or he could have his guy do it and send us a bill.

Overall a pleasant visit and he ended it by saying that he would let us know what his timeline was for listing the house.

A few days later he sends us a long email detailing 7 different "violations" of the lease including:
-cigarette butts (no problem, easy fix)
-tire tracks in front of the drive way (from the mailman)
-the roof is not swept (???)
-states that he has heard that there are often 5 cars in the driveway (lease stipulates 6)
-finally he claims he never authorized the 4th roomate

He finished up the email by saying he wanted us to pay him $400 extra a month and agree to only have 2 cars in the driveway, sweep the roof, etc. We have 2 more months left on the lease and he is demanding we pay him the full $800 immediately even though we pay rent month to month.

The lease has a "default clause" and and "early termination" clause that specifies we get 60 days notice to move out. My question is if he considers us in "default" does that "early termination by landlord" still apply?

Can we tell him hey there's only 2 months left on the lease, we will pay the regular rent for the duration of the lease and be out in 60 days?

Sorry for the massive wall of text...