Judging the living and the dead
Are souls of deceased believers in heaven now? If so, wouldn't that mean their judgement day was when they died instead of when God comes back to judge the living and the dead?
Yes, the souls of Christians who have died are in heaven now. When death takes place, judgment also takes place (Hebrews 9:27). Jesus promised the repentant thief that he would be in heaven that very day (Luke 23:43). The book of Revelation describes Christians in heaven who were killed for their faith (Revelation 6:9-11).
On the Last Day, when Jesus returns visibly to this world, he will judge all people (Matthew 25:31-46). Those who died prior to the Last Day received judgment when they died. On the Last Day, that judgment will be made public. Those who are alive on the Last Day will be judged at that time.
When we know Jesus Christ in faith as our Savior, we know what the Judge will say to us whenever we appear before him. That is our joy and confidence.