Returning extra money that one received as a refund

Q: I live in a rented apartment in the UK. Before renting an apartment in UK, we have to pay a deposit which is refundable when we leave the apartment. By mistake my landlord created 2 deposits and I got twice the money back when I left the apartment. I contacted my landlord and told them that this was a mistake on their part and they told me they will contact me soon about this issue. They haven’t contacted me yet. Since I have done my duty of informing them and if they don’t ask for it back or claim it, is it halaal for me to keep the money?

Zakaat on crops

Q: We got a land as inheritance from my father: a portion of which he inherited from his mother and the rest of the land was purchased by my father from his heirs i.e my uncles. His mother also received the land as inheritance.

Zaid is living on this land and whatever vegetables, crops are grown there, I am responsible for providing the seeds and other expenses. Zaid looks after them, sells them in the market and then the profit is distributed as a 50 percent share. From the 50 percent that we receive, it is further divided into 8 parts, one part is received by 3 sisters and my mother each. While 2,2 parts belong to me and my brother.

Previously rainfall was the source of water for this land but almost 6 months ago we purchased a motor to draw water from the small natural water stream that passes through the land. The land is not plain, instead it has many small hills in it so the irrigated portion is quite less. Sometimes I get only a little portion of vegetables that cannot be sold so its used at home.

I want to inquire how to give ushar on the produce from this land?