Situation A:
We even as the bishop, wouldn't have a right to tell them they're not in love. I think pre marriage discussions with them, where there can be an open dialogue, is definitely in order. As Bishop, I would ensure that a temple recommend wouldn't be issued immediately, prayer, and reflection on the situation is definitely needed. After all is said and done, and the feelings are all the same, then I think it is their right to continue with the ordinances.
Situation B:
Prenups are nothing more than a statement of "what's mine is mine, and what's yours is yours". A marriage that has the love, and caring needed to succeed, doesn't start that way. In my opinion the engagement would be ended if the roles were reversed.
For situation A I will be very suspicious. For situation B I will have to consider it a sign that he isn't sure he wants to marry or does not trust me fully. I probably will not sign it.
For situation A, if the couple loves each other, and want to get married, there is no reason that I would deny them a temple marriage.
For situation B, that is harder to say. I watched a documentary by an heir to the Johnson & Johnson fortune. In it he interviewed lots of children, who were born wealthy. They all said the same thing. Their parents drilled into them, since childhood, to get a pre-nup, if love tells you that you don't need one, you can always find some millionaire, or billionaire, who did NOT get a pre-nup, and had everything taken away from them. If I was dating someone who is wealthy and wanted a pre-nup, I would try and find out the reason, and would be open to signing a fair agreement.