Click on 'Add Spouse' just above the man's name to add the 2nd wife. It's best to add by PID, to make sure you get the right person. The screen shot below shows George Bright with his two wives. When each relationship is added it will create another couple box.
That is not a problem/issue ...
Further to what 'Patricia' has already proffered ...
You can add MANY Spouses; or, none.
You can add MANY Children; or, none.
Or, ANY combination, of Spouses and/or Children; or, none.
You can even have Children in more that one Family (in fact, any number of Families), with different "Parent-Child" Relationships (ie. Biological; Adopted; Step; Foster; or Guardianship)
Child in MORE than one Family
I hope this helps.