froze = past tense (finished action) was/were freezing (continuous action in the past) Hundreds of people were freezing in the ice cold water. John froze to death (correct but understood as he literally died). John was freezing to death (continuous action; John could not be dead or alive). "Freezing to death" is a common phrase used in English to indicate that someone is cold.

Hundreds of people froze in the ice-cold water. This would mean that the people died in the water or as an exaggeration that they became very cold. Hundreds of people were frozen in the ice-cold water. For people to become frozen, the water would have to be frozen, too. So it would be ice. John froze to death. This is exactly how we would say that John died from the cold. John was freezing to death. This means that John was in the process of dying from the cold but that he is still alive. John was frozen to death. This could imply that someone deliberately froze John to death.

I believe all the questions are correct. The first and third sentences are making a statement of what HAS happened, e.g. I fell down yesterday. In the second and last sentence 'frozen' is describing the state that John and the people died in, that is- how they were found and in this case, they were FROZEN, e.g. when I FOUND the bike,it was broken. Finally, the fourth sentence is describing what is still happening presently for example, I am walking.