If you look at the Oak farm pics they might help. They are tricky to sex though. Even vets have trouble sexing them. Be sure you have the male out now as they mate right after birth and if he is not out then she will have yet another litter soon which is not good for her health.
I'd take the whole lot of the older pups out now as they will still try and suckle. Males can go in with dad and females in a group on their own. If you only have one or two girls they can stay with mum and will help with the new litter. Get all the males out though. Lots of useful robo info here though
Oak Farm Roborovskis
Males will usually have a small bit of fur between the two vents and females dont. You can sometimes see the nipples nearest the back in the females. You can often feel the testicles coming down in males. You need to scruff them to get a good look and dont be afraid to get a good grip of neck fur supporting them on your palm, Both will have a small nobble near the front vent so don't mistake that for the penis. It is the gap that is more important.