How, If child is in college, and a a mutual agreement between both parents and child, can child support case be closed in NJ?

You can enter into an agreement/consent order to address this but should use an attorney.

I have been separated for 2 years, but not divorced, is wife still entitled to my health insurance ?

Do not remove your wife from the health insurance unless it is proven she has her own or you obtain a divorce.

Unfortunately NJ is a no-fault state so she can obtain alimony but the good news is you are only married 2 years which is a very short marriage so...

My friend's ex-wife with theirs 3 kids lives in New Jersey. He has court ordered child support in the amount of $1100.

Contact an attorney but she cannot go back in time.

Do I need an attorney to help me complete the case information statement (CIS)?

You can do it yourself. It is pretty self explanatory and does not have to be perfect as some assets do not have estimates and other values move...

Is there any legal action that I can take against my ex wife who is spreading false allegations to my current wife?

Restraining order among other things

A parent who makes co-parenting very very difficult is enough basis to ask to change the primary custody?

He should file a motion if he has joint legal custody and set clear parameters of what she needs to tell him, when and how.

Yes you can. Need to get aggressive

Did you file? Do you live together? More information is needed Please provide or contact an attorney

Can I get mutual divorce while my wife is in India? Do I need her to be physically present to get the divorce here in USA?

Yes it can be done without her presence in the USA