Maybe don't apply to the same accommodation so you can have a bit of space from each other? It's probably up to you how involved you are in each others lives you are e.g. if you are both really into netball and join the team then yes you will have overlapping friends and may hear about what the other gets up to, but if you have different interests and courses you might not even see the other unless you arrange it. Lots of people can get homesick in their first few months of uni, being able to see your sibling if you are missing home a bit might be really helpful