This one says: He who has a wife and children, yet he does not own a house; he is renting; and he marries another wife while he has not established anything for his children and his first wife, does the person become sinful?
Yes, it is firstly upon him to establish that which is currently obligatory upon him. When Allaah the Glorified and High permitted polygyny He, the Glorified and Exalted, said:
فَإِنْ خِفْتُمْ أَلاَّ تَعْدِلُواْ فَوَاحِدَةً
But if you fear that you shall not be able to deal justly (with them), then only one. (An-Nisa 4:3)
So justice is one thing. However, that which is obligatory in terms of spending is another thing; that which is obligatory upon you in terms of spending upon them (i.e. the first family) is another thing. So if you do not give them their right or you do not have from wealth except that with which to establish their right and you want to marry another wife then we say: their right (i.e. the first family) right now takes precedence. And if Allaah blesses you (with more provisions) then marry; marry another wife. There is nothing at all to prevent you from that.
What is intended by justice between wives is as regards affairs of the Dunyaa which the person is able to divide. As for that which one is not able to divide, then this is the inclination of the heart. This is within the Hand of Allaah the Blessed and High. Allaah makes the hearts incline toward this one and away from that one; or towards that one and away from this one. The Prophet ﷺ used to say:
O Allaah, this is my division regarding that which I have control of. So do not punish me for that which I do not have control of.
And this is the inclination of the heart. Na’am, there is no harm (on the person regarding this).