I am sorry that I had to pare down your question. I would advise you to repost them so that you can get guidance for your exam.
The animals listen to Old Major's speech for a variety of reasons. The most fundamental of which is that Old Major's vision is a way for the animals to reconfigure the role they play in their world. Old Major is very pointed in how the animals are exploited by the humans such as Mr. Jones. For example, Old Major makes a pointed case that Boxer will be sent to the knacker when he is no longer of use. Old Major's vision is one where the animals are able to make sense of their suffering and be able to understand why they are in the position in which they are immersed. Another reason why the animals listen to Old Major is that he is seen as a figure of respect. Old Major's age and stature is one whereby he is perceived as one who has seen a great deal of life on the farm, so that his insights are meaningful to the animals. Another reason why the animals listen to Old Major is because he gives them not only the cause of why they are suffering, but a solution to their problems. His solution is that if the animals assert control of their own lives and of their own existence in owning the means of production on the farm, they will no longer be enslaved. This is a hopeful vision of the future, one in which the animals feel a certain level of redemption out of their present predicament of suffering. It is for these reasons that the animals listen to Old Major in the henhouse. He introduces the vocabulary of revolution to the animals, the catalyst for change.