Is it permissible to offer mandatory prayer while sitting?

All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions.                                                                                                                                                                                                                            Standing up is a pillar in the mandatory prayer and the prayer is not valid without it unless one cannot do it. As for Nafila (supererogatory prayer), one can perform it in the state of sitting even if he/she can stand, but his/her reward is half the reward of the person who prays while standing if he/sh has no legal excuse for such an act. And Allah Knows Best.

I took a car from the Orphans' Fund Development Institution; is there usury (Riba) involved in this transaction?

If the Sharia's conditions were met, then there is no harm in this. And Allah The Exalted Knows Best.

Is it permissible to move a grave from its current location to another place, for example, from a garden in a home to a cemetery, knowing that the grave has been there for a long time, about fifty years?

It is not permissible to move the deceased from his grave, as this may result in breaking his bones and violating his sanctity. Such actions are not allowed. And Allah Knows Best.

I am a doctor, and sometimes I refer patients to the hospital for surgical interventions, and they give me a commission from the fees of the surgeries, even though I do not perform these surgeries. What is the ruling?