How can one be absolved from the injustice done to the first wife who passed away, after divorcing her and marrying another, and what are the consequences of that on the Day of Resurrection?

You must repent of the illicit relationship with the woman before marrying her. Divorcing the first wife does not involve injustice if she receives her rightful legal dues. If you wronged her and she passed away, you must seek forgiveness for her and supplicate for her, and that will be sufficient, Allah willing.