Introduction contract:
The infamous Rufio has [censored] and killed the wife and daughter of Claudius Arcadia, who is in prison for conducting the ritual to arrange a assassination with the dark brotherhood

First contract:
Some rich merchants want him dead, because he's bad for business.

Second contract:
The nephew of Baenlin named Caenlin wanted the house for himself.

Third contract:
Your new family give you the opportunity to take revenge on Valen Dreth

Fourth contract:
This Breton has huge debts to underworld types and wants to escape the enforcers by faking his own death. He gave his mother's life for his own safety.

New contract giver

Fifth contract:
Maybe his girlfriend issued the contract, but that seems unlikely. Maybe a close friend/relative of Lorkmir who found out the truth?

Sixth contract:
A fellow warlord wants him dead, or some angry farmers who have there crops taken by Roderick's mercenaries.

Seventh contract:
I really don't know. I can't think why all six have done something bad to someone.

Eight contract:
Easy one. Adamus was investigating activities of the dark brotherhood. Know your new family wants to give him a "gift".

Ninth contract:
Clear out the sanctuary to be sure that none of the residents is the assassin among assassins.

Tenth contract:
Some mage from the mages guild found out and know a shadier person "took care" of the untransformed lich.

Eleventh contract:
The draconis family made someone very mad...

Next five contracts:
The assassin among assassins gave you this contracts, as you killed the whole black hand

The rest is obvious... I hope