maybe first thing to do is to take your brothers set up to the park to practise cause if he can cast it, it's not going to make that much of a difference by getting a different brand rod & reel to the shimano, you may still have the same problem. I use a number of set ups and if holding a heavy rod is a concern of yours, you could try the the 12ft silstar crystal blue / crystal power tip rated @ 8-12kg yet sensitive enough to feel bream bite and quite light. They are quite wippy and can cast a mile. I have my own pref. for reels,i like the daiwa emblem pro, okuma salina 11 10000 & 16000 which i use on a multitude of rods.
I'm not a bad caster but i was fishing with this guy once who had an overhead with a 9ft rod who outcast me. i couldn't believe my eyes ( just to throw another spanner in the worx)
cheers