As a handful of responses to my Psyker's situation. He's a cautious and paranoid individual by nature anyways.

As far as line of succession this noble family runs on matriarchal succession, so it's his wife that will inherit the title as head of the family, when her mother passes on, not him. Though obviously, at least in theory, he will have a name to swing around with some weight.

From what he has gathered, they do indeed intend to benefit from the fact he has Inquisitorial ties. Said nobleborn girl actually passed up the chance to marry the son of a Lord Commander. With regards to my own character, her father disapproves of the marriage, her mother is hesitant, but was in favor of the idea.

As far as why the Inquisitor would allow my character to go through with it, as mentioned he practically stumbled into it. Long string of coincidences. My character is the dutiful sort, who, when given a task will do everything in his power to complete it, regardless of unexpected surprises along the way. He met his future wife, at a party the Acolyte cell was infiltrating and ended up hitting it off with her. We found that the individuals we were investigating were targeting her for assassination. When the rest of the cell ended up following a Red Herring, my character managed to foil the assassination attempt and saved her life (much to the GM's surprise-- he'd had her slated to die in the attempt, and hadn't expected my character to be able to save her).

Later, we needed a way of cutting through the red tape to arrange a meeting with the planetary governor, so my character decided to see if he could use the "I saved your life" angle with the girl, to see if her family could use their influence on him. She answered that she was more than happy to do it, on the condition my character agree to marry her. My character is the dutiful sort, and saw this as a "small sacrifice" in the way of completing the assignment he was given, so he agreed, and well... my character keeps his promises. So now they're married.