Sorry you're having to go down this path.
I think generally they do not transfer more than one except under certain circumstances - like age and multiple failed cycles. Having more than one transferred doesn't necessarily increase the chances of success, but it does increase the chance of twins or higher-order multiples, which is a significant risk for mother and baby.
If you're wanting to look at this option, maybe it would help to talk with your doctor some more about it?
Good luck!