Does justice between wives mean equality in the duration of foreplay and the number of sexual encounters, and is it permissible to fondle one in front of the other or to be naked in their presence?

It is not obligatory to be just between two wives regarding the duration of foreplay or the number of times of intercourse. One wife should not be caressed in the presence of the other, nor should they undress in front of each other, as this goes against modesty. It is not permissible for one wife to see the forbidden 'awrah (intimate parts) of the other.