It is nothing new for your co-wives to argue and fight with one another. Upon you is to make each one feel as if she alone is the special one, the sweetest one, and the most beautiful one. And there is no harm in you lying in this regard. As the Prophet (saw) said:
“Lying is permissible only in three cases.” And one of them he mentioned was: “A husband (lying) in order to please his wife.“
So let each one of your wives feel as if they are the one who you love the most. Backbiting is indeed impermissible, so saying words like, “Honey, you do know I love you more than Faatimah and Safiyyah right?” Or when she does something which pleases you, say how she is the only one who can please you like that. And use your imagination, however make it sound as realistic as possible (I hope no sisters are reading this, lol).
When your wives are arguing with one another, it is upon you to bring about peace between the two of them. Allaah says:
“If two parties among the believers fall into quarrel, make peace between them…” [49:9]
Furthermore, the Prophet (saw) himself used to strive to reconcile between conflicting parties, regardless of how busy he was with the heavy duties of da’wah.
It is upon you, o husband to give equal share to each wife. And when/if you do take them out together, or if you are in a scenario when both of them are present with you, you should follow the guidance of the prophet (saw) and give each one a equal share of your time and happiness. One of the Companions described the Prophet saying:
“The Prophet (saw) used to give an equal share of his attention to each person present, so that no one would feel that preference was being given to anybody.” [Hayaat As-Sahaabah, 1/23]
Showing unequal love (or share of attention) to your co-wives (when they are both present with you) is something which you need to control. Don’t give sweet talk to one and give a cold shoulder to the other, as this only has bed consequences. Among which are:
1) It will add hatred to your wife’s heart for her other wife (who is receiving more love).
2) Due to this, she will feel left out and hence her sadness will be manifest by her not showing enough love to you, as she will feel there is no point as you obviously don’t love her as much as you do with her co-wife.
3) She may get envious of her co-wife which is a sin.
4) When problems between your co-wives comes to surface, you will be the one who will be stuck in the middle and who will have to sort it out.
So know, O husbands, that showing unbalanced love has great consequences.