Is the second wife entitled to demand that her husband's children be sent away to their mother, and if the husband refuses, is she entitled to leave the marital home or demand a divorce?

A husband does not have the right to force his wife to live with his family. If she refuses, she has the right to live in a separate home, as she may be harmed by them. It is your right to demand a separate dwelling from his children by the other wife. If the husband refuses, you have the right to leave the house until he provides you with a separate dwelling. If his refusal persists, you have the right to seek a divorce, with the reminder that divorce should only be resorted to after all means of reconciliation have failed, and that overlooking and compromising are preferable to separation.