Is it possible to repent from adultery after the two adulterers get married? And does Hajj expiate major sins?

Adultery is a grave sin. Those who commit it must offer sincere repentance to Allah by abandoning the sin, regretting it, and resolving never to return to it. Repentance erases sins. It is preferable for the adulterer to conceal their sin and not confess it, based on what was narrated from the Prophet, peace and blessings be upon him: "Avoid these abominations which Allah has forbidden. Whoever commits any of them should conceal himself with Allah's concealment and repent to Allah. For whoever reveals his misdeed to us, we will apply Allah's كتاب (law) upon him." There is no objection to the adulterer marrying the person with whom they committed adultery, if both have repented. Hajj is not a condition for the acceptance of repentance, but it is a means for the forgiveness of sins.