I was recently selling one lot of 100 shirts on eBay, and an agent from the UK
contacted me saying he will buy it by sending a check from his buyer
and tell me to send the excess money to him. I received 5
fake/counterfeit money orders of $950 after confirmed by the bank. He
then emailed me saying I will be sued if I do not pay him the excess
money.

I want to know if I will be charged of any kind of fraud from the bank
or whether I will be charged for anything in court. Are these scammers
serious when they talk about taking you to court, and is the buyer &
the agent actually the same person?

This is a pretty standard scam
- normally Nigerians are behind these

It sounds as if you are fortunate, often they send fake cheques that
get cleared by the bank, and the victim is left both out of pocket and
with the law looking at them - a few months later.

The purchaser and the agent are probably the same person, although
they do run 'tag teams' for some of their frauds.

Of course the scammer will not take you to court.
Have a look at these sites:

http://www.419legal.org/
www.scamvictimsunited.com 
www.fraudaid.com 

You also might feel like playing games with the scammer, there are
people who deliberately give them the run around - they can be quite
effective.