Dual sired litter can absolutely be done. I've seen it happen. Here's the problem as i see it, most of the times the female will impregnate one of the studs. And the litter will be from one of the sires. Especially is the breedings are done seperatly. What i would do is collect the 2 males at the same time and do Ai. Good luck with it and keep us posted on the progress.