1. Well unfortunately your son does not spine and for his cowardice only you and your wife has to face the ignominy at this age.
2. This lady is incorrigible and does not like to mend her ways.
3. Either you relent your effort further or your son come out of his slumber and thinking your conditions leave his own wife.
4. I do not think no amount of social or peer pressure can make this lady agree to stay jointly with all of you unless and until your son becomes a man and act like one.