Hey mummy, I'm sorry you've been feeling that way :( Don't be too upset, it's common because he's at the terrible two stage where he's trying to do everything on his own and explore everything!
From what you've mentioned, I think that it could be something that he's doing to attract your attention - especially that he's beating his little sister. Could it be that he's feeling that your attention has been on his sister, and so he just wants more attention from you?
If you feel that his behaviour may have been linked to having a younger sibling, then you can try to spend alone time with your son so that he doesn't feel like all your attention has been "stolen" by his sister :)
Other than that, I know it can be frustrating and makes you want to scold or beat your son - but try your best to talk calmly at his eye level with him, you can look up gentle parenting too! I know it doesn't sound right to try to "be nice" in such situations, but if your child is feeling bad, your scoldings/beating will just make him feel even worse.
Jena Lim Xiang Ying