What is the ruling of the religion and what is the uncle's purpose in converting the clinic into a prayer room, while he refuses a better alternative location, knowing that he only uses the clinic two days a week and the heirs seek to benefit from it commercially?

In a rental agreement (ijarah), a specific duration must be stipulated. If no duration is specified, and the two parties agree on a monthly or annual payment, then this is a "month-to-month" (mushaharah) rental, which is not binding on either party, and each has the right to terminate the contract.

Therefore, you have the right to prevent him from converting the clinic into a prayer room, and you have the right to terminate the contract. However, you should consider the right of your uncle, as he is like a father. It is best for benevolent people to mediate between you to accept an alternative location.

Allah the Almighty said: "Or were you witnesses when death approached Jacob, when he said to his sons, 'What will you worship after me?' They said, 'We will worship your God and the God of your fathers, Abraham and Ishmael and Isaac - one God. And to Him we are Muslims.'"