Jagamoe - can't recommend an app sorry, but there are plenty of good worksheets online. My DP is pretty clueless money wise, we'll be sitting down soon for a big chat about it all. I think having it written down on paper and in front of you both can help you both see where the money goes. Work out what your payments will be when you're together (try the online estimators), write that and his income down, and then ALL of your expenses. Have a 'must pay' for bills, rent, groceries, petrol, insurance etc; and a 'it'd be nice to have' list - eg Austar, smokes/drinks, etc. having the raw numbers in front of him (and seeing how much - or little - is left over after the 'must pays') will help him understand where the money is going, and that those items to keep up with his bro etc are really not viable.
Maybe setting some financial goals together might help too (eg save for a holiday/house deposit etc)
As for who pays what - you'll need to work that out between yourselves and in relation to what the bills are..