Columbo says: Mr kingston gets the rest of the estate, then the lawyer answes "it is meaningless, he rented that big house". So how is that possible that the estate was in uncle's will? if it was not his? please expplain, perhaps american law works different :)

I haven't seen it recently, maybe referring to the contents of the house but not the house?

An "estate" can refer a piece of property, home, etc. However, in legal terms, an "estate" also refers to all of the property that a deceased person owned: money, real estate, art, stocks and bonds, etc. Dale's uncle didn't own the house, and the rest of the estate's value was in the art collection which went to Edna. Dale therefore would end up with very little.

It always bothered me that the uncle could afford to pay rent on that massive mansion, yet he allegedly had no money outside of his art collection. Where was the money coming from for rent? I guess it works for the purposes of the tv show.