Is it normal for my sister to go in and out of my sister's room casually and come to my sister's room casually? Right?

If you are sisters, that's fine. It's really because you think there are boundaries. But if they are other sisters, there will be a gap between them. After all, they are still outsiders! But there are also many situations. For example, you have grown up, have your own thoughts, have privacy, and have a separate room, so sometimes it is better to say it. You are all grown up!

Since you care more, everyone has different ideas, so I suggest you communicate with your parents and say that you have grown up and have your own space. If only you cared more!