They will tend to wean themselves, usually by 5 or 6 weeks. They start eating solid food before this.
How old are the kits? Don't touch them before they are hopping around the cage on the own or mum WILL eat them.
Sexing bunnies is all about the ano-genital distance - the space between the holes! I will try to find you a picture. Basically it's easier when you have more than 1 to play with as you will likely be able to group them into sexes easier than if you were trying to decide about one.
If I search anything about bunnies and sex on the work computer I really fear what I will turn up.