Re: Is this typical 4 year-old behavior?
Four year olds can be rather hard to handle. Sometimes worse than the terrible twos.
As far as the bad words, I can only tell you that parents must set the example. It's very hard to reason with a 4 year old about things like this. Saying bad words in front of a child and then telling them they can't use that language because it's an adult word only serves to confuse them. My son started saying things he heard my husband say, and I had to set my husband straight and the bad language stopped around our son. There was no way I could tell him they are bad words and allow him to hear those words coming from daddy's mouth.
You said that your son was with your in-laws for some time. Did they tend to spoil him? If so, your son could be just doing what is natural when children are spoiled and acting out because he is used to getting his way, and now doesn't get his way all the time.
It is concerning to hear you talk about the way he is choking his sister and also bullying the other children at daycare. I know you are concerned about this. Sweetie, it may be a good idea to speak with your pediatrition about this. Let them know exactly what your son is doing. It may be that he needs to be tested/screened for ADD.
I do hope you are able to find some answers to your questions. I know you only want what's best for your family. Take care and keep checking back. You will get a ton of information and support here.