Can A Lease Agreement Be Verbal

HI My parents rent real estate by private owners in the last 2moths You will see the lease in the property for 6moths. The landlord then gives the keys and said you can move in today, so they pay him the rent and the deposit and they get no proof that they paid. Anyway, they now live there 3moths and the owner does not want them to give the signed lease, my parents are getting very uncomfortable because they are now afraid of having to leave one day and they were right, if we call him every day about it, he keeps calling him, you don`t need it and today he sends a letter „Leave on January because am happy not about that you want the agreement“ Any advance please?? My son did not sign an agreement with the owner, only verbally. The owner now sells property, and calls us the night before to say that someone sees the property the next day. My son works, so I have to do it because he can`t afford to take a break. The owner came yesterday with a friend and another real estate agent, but he told us it was a visit. He told me today that someone will see tomorrow. It`s not fair that he keeps doing it, I can have some advice please hello, a friend of mine just said she has to leave her rented house privately in two days, she has no hot water for more than 6 months and the property is quite wet, she asked her owner to fix the hot and humidity problems and it never did , did she ask for advice and they send someone to inspect the property in 2 days, her landlord learned and told her that he wanted her in 2 days, she has no lease and no real proof of rent, does she have any rights? She was diagnosed with a terminal brain tumor and has two young children, but her owner is tenacious that she has to leave I am a GDL student (recently graduated) who recently left my apartment due to the end of the rent (respect the 30-day deadline etc.). This was based on a verbal periodic rental agreement that corresponded to the factors mentioned above in your article (offer, acceptance and consideration by the payment of the monthly rent). We are currently arguing (not in court, but only at odds) over the fact that he is now refusing to repay the $250 bond due to my parents, agreed upon my move last September (2014).