[X] Keep Ser Bryan alive for now, in fact it might be better if Lord Blount makes a hard decision starting with this traitor first.
-[X] Approach Janna and try to convince her of the details of the scheme using your social skills and, admittedly, a vast power disparity. Then with the other hand offer salvation and hope. If she acts as a character witness you'll promise to make arrangements for her future fitting and commiserate to a noble-born scion of her status, with higher education or even magic open to her.
-[X] Depending on how that conversation goes you'll try to convince Lord Petyr of this treachery together. You will give her at least a little help with Air of Nobility and Voice of the Dragon, and if fear is the issue, a boost of magical courage like with Samwell and Edric, if necessary.
[X] Bottle ser Bryan, then use the greater ribbon of disguise to stumble out of the tavern, going for the outhouse if this Tavern uses one, in his appearance. If that's not possible, pretend to be going out looking for some "company" if it can be done subtly // we need to confuse the issue of his disappearance somehow.
-[X] sneak into the castle and investigate the dreams of the current lord, widowed lady, and Janna.