A small, still-learning child doing age-typical things like not sharing, smacking, biting etc isn't necessarily a cause for concern. But just cos it's "normal" doesn't mean you don't deal with it. They've reached a certain developmental stage which requires a response from you

Lots of things are labelled as "normal". Teenage angst, defiance, boundary-pushing is normal. You still need to address it in some way.

You decide what your family's version of "normal" is, whether by action or inaction. If you don't actively manage it, "normal" happens anyway. Constant fighting, bickering, unkindness, selfishness does not have be your normal.

Actively deciding your normal means that the very first time the smallest child does something they shouldn't, you address it. You don't laugh. It's not cute to pull the dog's ears or bite a sibling. Doesn't matter if you think they don't understand

Addressing "bad" behaviour in small children about consistency & getting them (and you) used to those conversations: if you don't start doing it immediately, you'll miss the point at which it's become too late.

All of this assumes, of course, that you yourself behave & treat others in the way you want your children to. "Do as I say, not as I do" does not work. Be who you want them to be.

Common sense practical tips:
1. Don't tease children. They're not for your entertainment
2. Don't complain about them to others in their presence
3. Reprimand in private, as far as possible
4. Stay consistent: if hitting is not ok, it's never ok

5. If you shout for everything, you have nowhere to escalate to when it's really necessary
6. Don't be afraid of explaining how their behaviour makes you feel. Empathy comes from hearing that.
7. Talk about behaviour you see in others, both children & adults. Discuss it.

8. Every rule must have a reason. If it doesn't, it's a kak rule
9. Apologise freely. They can't learn how if they never see it done
10. Make sure they know that you are their safe place. Don't leave this one to chance. Tell them often, and show them.