If my assumption is true -- that the monitors are used primarily for vocals, with no or minimal reinforcement of instruments -- I'd ignore the monitors almost entirely. Wherever you are, as long as you're not waaaay up close and under the monitors (like stage height), should be fine for capturing the vocals. You're going to pick up most of your sound from the stage, so I'd position myself and / or my mics accordingly to achieve the best direct sound and balance as possible. It looks like the stage is in the corner, on a bit of an angle. I'd probably wear the mics and set up 2nd or 3rd seated person to the left of the gray-haired guy standing up, oriented towards the center of the stage.
Alternatively, you might also consider clamping to what looks like a pole hanging down from the ceiling behind the ceiling fan. Might require some effort to run the cables to a suitable place for your recorder, though, and I don't know if the house will give you the run of the place to do so.
Re the tin canny vocals...how did they sound in the venue? My experience is that for small stages with small monitors, the vocals never sound particularly good, and often produce a tin canny sound.
Challenging space, for sure.