You wouldn't refer to someone as 'my small brother', unless you were pointing out the fact that he is short in stature. "Small" is the opposite of 'tall' or 'large', and doesn't have much to do with age. In English, we can say 'older brother' or 'younger brother'. 'Big brother' and 'little brother' are alternatives in informal contexts, especially if you want to show affection. For example, a newspaper article might refer to someone's 'younger brother', but in conversation, you might say "I'm so proud of my little brother." BUT - and this is the important point - we usually don't. This is a significant cultural difference between most Asian and Western societies. Family heirarchies and relative seniority within families is a key issue in many Asian cultures, and you have complex vocabulary to match. This is not the case in Western culture. Nobody really knows or cares whether your brother is older or younger than you, and we rarely need to specify. If you're a child or a teenager, the relative age of your siblings will be obvious, so there is no need to mention it. If you're an adult, it really doesn't matter most of the time. If you happen to have two brothers, one older and one younger, you could distinguish between them in this way e.g. 'My brother Nick's getting married; 'Nick? Is that your older brother?' 'No, it's my younger one.'. But that would be one of the rare occasions when we'd use these terms. Most of the time, we simply say 'brother' or 'sister'. Please don't feel that you need to specify your relative ages or that you have to translate a specific term in your language into an equally specific one in English. It's fine just to say 'my brother'.

Hello, when speaking of our siblings, we say older/younger brother/sister or big/little brother/sister, but never small brother/sister. Hope that helps!