How can injustice be redressed for a former wife after their divorce and each of them marrying someone else? And can Allah unite an unjust man with a righteous woman? And is delayed childbearing a punishment? And how can one repent from that?

If a separation occurred between you, you must repent if you wronged her. The original principle is that repentance is achieved by seeking her forgiveness and asking for her pardon, as the Prophet, peace and blessings be upon him, said: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no dinar or dirham." However, since she is now married, it is not appropriate to contact her except with her husband's permission. Therefore, in this situation, it is sufficient to supplicate for her and frequently ask Allah to accept your repentance concerning her rights. If there was a material wrong, then the right must be returned or forgiveness for it obtained.

There is no necessary correlation between the righteousness or corruption of spouses. Your deprivation of a child might be due to sins, such as your previous wrongdoings. Seeking forgiveness and repentance bring provision and children, as Allah, the Most High, says: "And said, 'Ask forgiveness of your Lord. Indeed, He is ever Forgiving. He will send [rain from] the sky upon you in [copious] showers and give you increase in wealth and children and make for you gardens and make for you rivers.'" Therefore, you must repent and seek forgiveness, and also take the physical means necessary for procreation.