Cass I just want to say what a big heart you have for choosing to help your family in this way...

It's not easy parenting a 14yo. I have a 13yo daughter - & it's a challenge! She receives a $30 phone card a month and $20 spending money/month. In order to receive it she has to finish her alloted chores without needing to be reminded. She only failed to do that once!
What I have learned is that you need to remain calm and act with love and dignity at all times. Always speak more quietly than is needed - it somehow deflates a situation - the listener has to listen more to hear iykwim.
I don't use punishment - it's my opinion that consequences work better. Having a family meeting and asking the children or child to decide an appropriate consequence to an action has more effect.
For example my daughter decided that an appropriate consequence to not unpacking the dishwasher would be for me to not do one of my jobs - she decided the job would be that I would not drive her to swimming.... Mmmm that was interesting but I thought it was similar in that both were acts of service to the family. As I said she only did it once.
Also one of the rules is that her mobile phone is kept on top of the piano from 7pm - so there is no late night texting and phone calls. She decided an appropriate action for this would be that she woud not have access to her phone for 48 hours.

So maybe this would help with your brother. Firm boundaries that he has set. I have learnt that it is of little benefit and becomes arbitary and reactionary if we dole out punishment. But if an action has an agreed consequence it takes the "punishment" feel out of it. It also helps set him up for life. In life if you steal money - nobody trusts you so put to him "what would be an appropriate reaction". "Would it be fair to withhold allowance money"? "Would it be fair for you to need to do more jobs in order to "work it off"?????. At first he will need help with coming to appropriate consequences but with your help he will get it.

Good luck with your new role!