Recording A Cappella Trio

Hi All,
I have three friends in an a cappella trio and they have asked that I help record/mix some demo tracks for them. I want to help but my own music is mostly instrumental. So I'm wondering what kind of miking techniques you folks would recommend.
 
I'm pretty sure my friends would be perfectly happy with a single mic for all three (and I would add a couple room mics). It occurs to me that three mics would give me a lot more leeway when it comes to mixing but I really do not have the background where I feel I could make intelligent decisions.
 
Do any of you have any recommendations? I'd sure appreciate any ideas or, really, just a discussion. I have a fairly limited mic locker (2 SM57s, 1 Royer 101, 1 Mojave MA200) but they're good friends so I suppose mic rental might be an option.
 
Thanks much...