Fear rule and combat order.

Just wondering when charged by someone causing fear, I have to roll for leadership, if I fail I can only hit on 6's in the first round.

Is every round afterwards the same? Do I roll for leadersip every round?

And if one skaven is fighting three undead, in my turn I get 1 attack so I attack one of the zombies, they all in turn get one attack back at me. During the zombies turn, do I still only get 1 attack amongst the group of 3 or can I attack each zombie once as they attack me?

One last question, if I charge with three rats against one enemy model, can I pick who attacks first since they will all be able to "strike first" since they are charging?

Thanks in advance. I'm just a new guy.

To answer the fear question:
Page 23 of the rulebook says:
"Test when the charge is declared and is determined to be within range. If the test is passed the model may fight as normal. If it is failed, the model must roll 6s to score hits in that round of combat."

You only test for fear when you are charged by a fear causing enemy, so this applies only to the first turn of close combat. In the following turns you attack as normal...unless you are charged by another fear causing model. Note that if you are in combat against both fear and non fear causing enemies and fail your test you hit all of them only on a 6.

On to your second question:
You always only get your own attacks, one in the example you referred to. This is the same no matter whose turn it is. You can choose which of your three opponents you attack, but that´s it.

And to your last question:
Yes you can choose the order of the attacks. You can do this in all rounds of combat as long as the initiative of your fighting models is the same (which it should be with three rats).

I hope this helps you a little bit.