Lots of different experiences about hatching quail eggs under chickens - I've never tried, but from old posts on this forum and elsewhere, sometimes everything is fine, sometimes the hen squashes the chicks, sometimes the hen doesn't recognize the quail chicks as her offspring, sometimes the chicks don't recognize the hen as their mother (personally I find that unlikely, if she hatched them and she is warm I don't think they care one bit about what sounds she make or what she looks like). And sometimes quail catch diseases from chickens. With a bantam, I guess she is less likely to squash the chicks, but lots of things could go wrong, even if the hen does a good job. They could drown in the water, for instance. Or get stuck in some little crack somewhere. So I can't really tell you "they'll be fine, don't worry".. But they might.
