Is selling a inherited piece of land to one of the siblings – who already owns a share in it – with the agreement of the heirs that the land he will buy for us be considered usury, and how can usury be avoided in this case while providing liquidity to the sibling?

What you wish to do is a deception of the bank and leads to usury (riba). The deception lies in the fact that if the bank knew the land would remain your property, it would not have entered into the murabaha (cost-plus financing) transaction. This is considered deception, and deceit and trickery lead to the Hellfire.

As for usury (riba): This is because the bank will give you money and reclaim it with an increase without a genuine sale of the land. This is forbidden usury, and Allah has declared war on those who engage in it. The Prophet, peace and blessings be upon him, cursed the one who consumes usury and the one who feeds it.

And if your brother were to buy the land and then sell it to you, this would be a forbidden usurious 'inah (buy-back) sale. It is not permissible for the client to be the original owner of the commodity.

If you need money without selling your land, you can purchase land or permissible shares in installments from the bank and sell them for cash to a third party.