I 14 yr old I have used a condom and my bro has not used one and he is 15 yr old
So what is your question? Are you asking if that's normal ?
That's his personal choice. It's awesome you're doing what you can to prevent pregnancy and reduce the risk of an STI.
You could calmly discuss this with him and maybe he could why he's not using condoms. Yet, on the flip side, it may do more harm than good.