Ariosto wrote:.... Depending on the room/hall acoustics I might close mic the grand piano (with the lid up) in stereo, and have either a separate mic on violin and voice, and space the player the right distance to get the best sound. ...
Where does it say that it's a grand piano?
I've not found grand pianos particularly common in church halls; several electronic 'pianos' of varying quality, lots of uprights, occasional baby/boudoir grands but very few full sized grand pianos and, with one exception, they were pretty rough.
Whatever type of piano you have (give or take the electronics), it’d almost certainly be worth getting it tuned before recording it as nothing makes for a rubbish listening experience quite like an out of tune piano. It also makes it harder for people to be accompanied by or to play in a group with. I’ve lost count of the times I’ve been told that a church hall/church piano won’t need tuning because they have it tuned regularly and it never goes out of tune, only to find that ‘regularly’ means annually and the only reason it “never goes out of tune” is that no-one who listens to it has a clue whether or not it’s remotely in tune!
My experience of recording in church halls is that, with few exceptions, they tend to be lots of hard surfaces and parallel walls making a nasty, overly reflective, clangy, acoustic mess of early reflections and flutter echoes with, maybe, a bit of damping in the form of window curtains or maybe a nice heavy stage curtain.
Regardless of the curtains/not, if the floor is hard it’d probably be worth taking some rugs or large bits of carpet to put under the performers/mic positions to help clean up the earliest of the floor reflections. If the hall has movable chairs, it’s often worth making sure that at least some of them are actually in the room and set out (covering maybe half-ish of the floor area?) since they break up the reflection patterns a bit compared to a big empty floor. If they have fabric upholstery they can help damp an overly reflective space but even the traditional plastic bucket seats can help break up the fluttery/slappy reflections.
Also, I didn't see from the OP whether this is actually recording everyone together as an ensemble or are they playing individually, with/without piano accompaniment?