They ask lots and lots of questions at these trials which is why they drag on for months. I would assume the Crown will try to argue that CN was ready and willing to do DM's bidding. In that kind of scenario, if she accepted expensive gifts (beyond the vacations we already know about) that would certainly be relevant.
Re the ex-fiancee, she was a big financial beneficiary, but I have no reason to believe her mother was on the unofficial DM payroll.
And, yes, as far as I know, both the ex-fiancee and Mom are still supporting DM, and so too are some of his friends.
I think you're over simplifying the nature of DM's relationships. The people who were buddy buddy with DM and financially benefited from their friendships with him have a lot to potentially lose if he is eventually found guilty.
They will be asked constantly what they knew, what they saw, what they overlooked, what they gained. There will be shame involved in being known as the financially beneficiary of a murderer (again, if he is found guilty). People will be asking, how they could not have seen, whether they were blinded by the money. A lot of people have a lot to lose in this situation.
As an analogy, you might want to think of this like sleeping your way to the top. It's complicated and not something you want to be known for.