Thanks guys. I managed to achieve it, but I had to use pliers to hold it in the middle to get the last nut off (the bottom one of the two that I used to take off the stuck one). I had difficulty getting the bolt back into the hub fully as well. It was hard to get two nuts on. I only had the OEM sprocket nuts.. and to fit two on with enough purchase on the top one was tough.

Thanks to your help, I managed to get the sprocket done, cleaned the rear brake up, got the wheel back on and torqued the front sprocket properly. All I gotta do now is rivet the chain and tension it and the bike is functioning normally again!