Responses
It's a common practice to ensure that noble bloodlines don't get extinguished easily. Most would end up with 4 or 5, but the children of anyone past the third wife often picks up a different trade or path because inheritance is stronger between the first and the third.
Sometimes they even work at the main house when they come of age and serve the current or next heir.
Are we ignoring the fact that he said second wife and that the main one is alive, with a kid and in the capital?