If you are serious, and I think you are, you and your brother should do a step test to identify your anaerobic thresholds. It's mostly just going to be fun. You need a bike, a heart rate monitor, stop watch, pencil, paper, and somewhere to ride about a five or ten minute lap. And google, to figure out how to do it.

I like the linear/plateau test, but you might get more accurate results with the 2 x 20 test which is stickied in some subforum around here somewhere.

Once you figure that stuff out, you need to train at proper intervals at proper heart rates, and hopefully you will get stronger.

Then again, maybe you are dying.