Bigger isn't better. Being VERY honest, the space you record in depends on the musicianship. If you have a gorgeous sounding church, and a professional orchestra, then it will record wonderfully. However, if you intend doing editing, then the church is NOT the place to record at all.
I'll try to explain. My colleague is a concert pianist - we work together often. At first we recorded beginning to end. He'd detect a tiny mistake in a piece of karate fingering Shumann and want to re-record, but he'd start tiring and make more mistakes. Eventually I convinced him we could record in sections and then edit them together seamlessly. His Yamaha is in a normal sitting room, with heavy velvet curtains, carpets and soft furnishings - it's quite dead and rather dull to record in. We then add artificial reverb to the finished thing so the room sounds bigger and nicer. You will find the same thing with your two strings and piano. You need to decide what you want. Can you all play it at the standard you want reliably. With three people, rather than an orchestra, mistakes are VERY obvious. How do you fix them?
I suppose I'm really saying do you cheater not. Cheat in a technical manner, not in a deceitful manner.
If the room is a bit live - how does it sound with you all in it? Boxy - deafening? How do the musicians feel about using technology to improve their sound, above what it really was?
If the cello plays flat on a note - if it has spilled into the violin or piano mics, you cannot fix it, because the pitch shift will impact on the fixed pitch piano.
If the musicians are willing - you could record all three instruments as a guide, then one by one, re-record the individual parts which could then be edited. Some will love this, others hate it. For strings, and brass - I prefer a deader acoustic in a smaller room because I can make it bigger. Recording on location is never as much fun as in your studio.
Beware of the musicians who need the reverb in the room to play properly. Strings play off each other tuning wise for that chorus-ensemble effect. That's difficult in dead rooms. Unless you have a decent acoustic in a big room of your own, I'd definitely go dead and make it sound nice afterwards. Churches can be great, but you really need to get a pair of speakers in a vestry so you can really listen. This means a video link and talkback to be effective - and you need to listen for vehicles passing, bird noises and all the other rubbish collected by mics in non-studios.