in my humble opinion, forget the sparring for a while. work on kicks with focus pads and a bag. also, get some arm pads and let your bro kick as hard as he can right to your mid section (not off to the side) like he is really trying to hit you. with the arm pads, you can block without breaking anything. learn to block by *deflecting* the kicks, don't meet the kicks head on with your forearm.
You have to get the basics down so that you can spar with power and not worry about getting hurt or hurting the other person. protective gear is always a good idea until you really get safer blocking down cold.
also, don't forget about the principals in the SD techniques that you first showed....in those techniques, did you step back and then step in? no. you held your ground and stepped in. later, you won't even wait for the attack to finish...you should be able to step in before his attack is even finished...this is a very effective tactic in sparring- always throws people off.
tactics like:
he kicks, you step back.
he kicks, you step back.
he kicks again, and you step forward while guiding his kick off and counter even before his foot hits the ground.

just a few more things to think about...