How should a person who drowned or burnt to death be given ghusal?

Q:

1. If a person’s body was completely burnt, how should one carry out the ghusal?

2. Similarly, how should ghusal be carried out in cases where it is difficult to perform the ghusal (e.g. advanced stages of decomposition or a person drowned and his body was recovered after many days, due to which the flesh and skin are coming apart and disintegrating)?

Will a shaheed be given ghusal?

Q: If a person is murdered (and gains martyrdom) then can ghusal be given to his body? In many cases, post mortem is conducted by non-muslim doctors and najaasat could have come onto the body. Also, it is possible that ghusal could have been waajib on the deceased at the time of his death. Will these factors affect the mas'alah in any way?