Can a landlord change a lease 3 days before move-in? (Tenants signed earlier,but apparently landlord didn't?!)?

Since the landlord never signed the lease, they didn't agree to the terms you signed for. Personally, I wouldn't rent from someone like this. I have rented a lot and have dealt with jerk landlords. This will only be the beginning. A landlord such as what you are dealing with will cause you problems at every turn (won't fix things, will try to keep your deposit, etc). I'd get a hotel room and look for another place.