Do I have to pay them

Not unless they file formal suit. You might keep getting letters though.

Is possession of a small amount of marijuana (25 grams or less) for personal use only a violation in NYC and NY state?

Yes it's true, but it doesn't mean that it is legal. Marijuana convictions, even if non criminal, can have severe collateral consequences.

If your acd is still pending them the da can reinstate those charges and you would ace 2 separate cases.

My friend wants to come out and tell the truth, he was high on drugs and wants to know what he's facing.

You posted about this before. Your "friend" needs to speak with an attorney in person where he can get specifically tailored advice.

Do I need a lawyer to help close the case? How do I start the process to this situation? Is there a possibility of an arrest?

If someone has an open case then they need a lawyer.

Can one motion for a case to be dismissed at arraignment?

If you made a proper demand for a supporting deposition and have not received it within 30 days then a motion to dismiss would be appropriate. If...

My question is with lack of evidence and testimony, will my father be able to have a retrial or file for a lawsuit?

Too late to appeal. Why didn't you come forward back then? That was the time to fight this.

What can I do to have this attorney fulfill his word? And should I t hire an attorney to look into his actions?

What was the promise? The fact that your attorney changed jobs after representing you does not mean he didn't represent you properly. You will need...

What kind of sentence will i get?

You need to get a criminal attorney. You are probably not going to jail but a criminal record for theft can ruin your future. What employer do you...

What will happen to me in court

Sounds like you will be charged with assault. I suggest you retain a criminal attorney immediately.