The property in question has already been foreclosed on, and at the time of the foreclosure, there was no lease, verbal or otherwise, and the property was not in the landlords name but in someone else's, who has the right to try and sue? Also, what proof is needed to sue someone, when the landlord was fraudulent about the property being in foreclosure?

With no lease you were a month to month tenant. What specicifc fraudulent behavior are you talking about, who did what to who? What damages were suffered by the party that wants to sue, monitary damages.

1. the landlord has no obligation to tell you that a property is in foreclosure

2. they may not rent property they do not own or have a legal right to rent.
** so if they rented you a property, that they did not own on the date the rental started, they committed a fraud,
*** if they rented the property knowing it was going to go to be foreclosed on, it is just unethical but not illegal yet.

Once it is deeded to someone else, ( a bank or mortgage company or a new owner) then they own the property and any rent should be paid to them, not the old landlord.
Any lease is voided at the foreclosure but under federal laws they normally have to give 90 days to evict