Is the second wife's demand that the children from the first wife be brought to her home considered coercion and injustice to their mother, and is the husband entitled to take them without her consent?

There is no harm in a husband taking his children from his first wife to his second, or vice-versa, and he is not obligated to seek permission. It is good upbringing for the relationship between the children and their father's wife to be good, as they are her mahram. The second wife is not to be blamed for her desire for her children to socialize with her husband's children, which necessitates her honoring her husband's children so that the children grow up loving their father's wife.