Obstruction and Interference
 

Can you please tell me what a catcher can't say to a batter? EX - While the pitch is in the air, can the catcher say strike, swing.

If a runner is rounding second, on his way to third, when the SS fields the ball - Can the runner yell throw to first or home?

I might be reading to much in to the rules but IMO these examples create confusion.

Any Help Please!

In the examples you have, I don't think I would have a problem. I might have obstruction or interference if a player was yelling things like, "foul ball" or "time" or other words reserved for the umpire.

In your example of "strike", I don't see this as a problem because I'm presuming the PU calls it after delivery. (First base coaches seem to yell "safe" a lot also.) If it gets too out of hand I might ask them to knock it off.

The catcher shouldn't be saying anything to the batter while the pitch is on the way.

If they do, they may be subject to an interference call if the umpire judges it to have affected the SS's ability to execute the play

In most cases, I don't have a problem with catchers if its simple chatter. If the catcher were to say something like "wait" or 'no stop hold on" I would be talking to him/her.
In the second example, it is a good chance that I would have Interference. Of course, it would depend on the play. If you called it once, I doubt the runner would try it again...at least until the next game and a new batch of umpires.

If a runner is that close to a fielder and yelling those kinds of things to/at him, I am VERY probably calling him out for interference. That is exactly the kind of thing the interference rule is intended to prohibit when it makes reference to any act that may interfere with the defenses chance to make a play.