I am not a muslim but i have a best friend whose faith is ISLAM... he is like a brother to me , we know each other since childhood.
he has 3 wives...in his succeeding merriages , meaning 2nd and third marriages, he prepared emotionally because there were process to be done which is an unwritten law , meaning you have to sit down with your first wife and ask his consent wheher she is amenable for his second marriage , same process will be done onwards up to 5 marriages as the law allows.

he prepared emotionally because in that case two things may happened whether the wife will say YES OR NO.

I ask him why ? he said i am doing this as my respect to my original wife , blessings come if the family is in union and respect each other.

my point is better to ask the consent , as a sign of respect for each other.