I am sorry to hear the vets, in your area, didn't have more to offer you
and the conflicting information from previous owners.
When I've had our mares estrone sulfate test taken I've had the results
back no later than the next day.
I guess the ball in your court, now. You'll have to do the
watching for the mare and keep your little girls and your excitement in check,
till you're sure it a no go or a go.
Darn.
Things can change quickly, at the end of a pregnancy but at least you do have
a stall to bring her to in the case of a blessed event.
You might keep a camera handy to photograph her bag, so you can keep a very
accurate record of any potential development, rather than leaving it to
memory. Bags aren't the last word in confirmation of pregnancy, for some
mares, but it's better than having nothing to go by.
Hang in there.