It was an ordinary house, he thought, an ugly house, nothing to boast of. But the idea that it was his, the idea of family history pleased him.
In this passage, the narrator is describing Edmund's feelings about Warings, the house in which he lives. These feelings turn out to be very important, because they explain why Edmund is so very defensive of his home, and so very resistant to the idea of Charles coming to live in it. There is a saying that an Englishman's home is his castle, and to Edmund, Warings is his castle, and he is going to defend it at all costs.
Charles is not just moving into a house. From Edmund's perspective, he is moving in on his family, and on his role as son and heir of the Hooper family. There is stature and history involved in Edmund's perception of the house and he does not see why a stranger should be able to come into the house and have what Edmund has. Edmund is protecting his own line and ot him, Warings is an extension of that. Longevity means something, even if the house itself isn't much to look at, the fact that it has been there and in his family a very long time gives the Hoopers a stature that others don't have.
He hated his mother more than anybody, more even than Hooper, now. He had a terrible twisted-up feeling in his belly, because of it.
When Charles finds out that his mother is going to marry Edmund's father, he feels an immediate hatred towards her for the decision because he knows it is going to ruin his life. He is enduring Edmund's bullying at home, but he knows that the two boys, who come from very different circumstances, will be attending different schools once the school year starts again. He will have some respite from Edmund's bullying.
When he learns that they are to become step-brothers, and that they will attend the same school, he is terrified and he cannot see a way out, or any hope, because he knows that the bullying will continue and that neither of their parents will do anything about it. Charles is not in control of his life, but controlled by his mother's decisions for them both. He is trapped.
