Well, I think your buns are very young and this take times. And even then, once the hormones kick them, they will probably go back to marking their territory, especially since there are two of them! Make sure the litter box is big enough for both (I can’t remember if you house them together or not…). Add some hay to the box, bunnies love to eat and poo at the same time. You might also try adding a fresh green veggie to entice them.
Ah yes carpet. There are a couple things you can try: 1) make a very loud noise when you see them digging/chewing it. It should startle them. Do NOT chase your bunny away. Bunnies, as prey animals, don’t like to be chased. It will make them fear you. I find the noise things works to varying degrees depending on the bun. 2) Water pistol. Most bun hate getting wet so sometimes one quick squirt across the back distracts them and they forget about the carpet and soon learn to stay away from that spot. However, sometimes the water pistol just annoys them. Again, varying degrees of success. 3) Put something heavy over top the one spot they seem most interested in. A box, a tunnel, a sleeping pad, anything else. 4) Spray the area with something bunnies hate. I used regular yellow Dial soap. Cinnabun hated the smell and the taste enough that she ran in the opposite direction. You can also try “no bite” spray typically found at pet stores.