That's a direct plan, kahn. It could work well, but there is a chance that we meet stiff resistance if Owen is in the Keep with a knot of diehard supporters, and then almost the entire city will be wondering what the hell is happening over there, and unsure whether we are invaders to be resisted or not.
This is what I see... Recapping from above, we put all of our rangers and Oswald in the gatehouse. It appears that the gate guards are with us, but let's give them a lot of help to stiffen their spines. For now, our men can catch some sleep inside during the night, holding watches.
Next, somewhere in the city is an armoury for outfitting a levy much larger than just a city watch and a handful of retainers, so let's get that building under our thumb tonight, as the first thing done inside. Uriel is definitely in direct line of command above the guards and officers here. They have no reason to disobey his commands for now, at least. Our men fortify the armoury and likewise catch some sleep in watches, Finn commanding. We lords and claimant have a bit less rest, as we and a small escort including Luther and the heavy men-at-arms of Uriel must do the rounds tonight, riding about and trying to persuade the important people, such as the mayor and the guard captain first, then the officers of the levy that Uriel himself would control but need to be brought on board for certain. We tell them that we muster at first light at the arsenal and march to the Keep.
Depending on our sense of the success of this, we may have to send a message to the Rat instead to whip up a mob and march to the arsenal at first light to be equipped. I'd prefer that we tap the officers of the levy to raise trained militia to be outfitted in our name, though. Either way, no large group is getting equipped in that city but our supporters. That's my plan for this operation until something unexpected can obliterate it. It delays the action till morning and broadens the base of people that know what we are about.