There is only one mediator and that is the Lord Jesus Christ:
1 Timothy 2:5 For there is one God, and one mediator between God and men, the man Christ Jesus
When we die, we are DEAD. There is no hope for life after death except for the resurrection when Jesus returns to establish his Father's Kingdom on earth. The faithful dead are in their graves awaiting the resurrection. They are not conscious so they cannot mediate anything.
Here are links to information on our system which you will find very helpful:
After Death, What? www.thisisyourbible.com/library/show/43
The Kingdom of God: www.thisisyourbible.com/library/show/170
I hope you have found this helpful.