My nephews girlfriend ran her car that's registered in her mother's name into my house causing damage to my house.

Hopefully the girlfriend carries some insurance on another vehicle that cover her driving. Otherwise, you will have to file suit against her an/or...

What should I expect

Retain a local criminal defense lawyer. You are facing license suspension with the hit skip. Based on the facts your attorney might be able to...

Your lack of a license has no impact on the true issue of fault. The insurance may try to pay less because of it, but it is not relevant.

Should I try to get a bigger settlement check?

You may try to negotiate for more with the insurance. You may be able to get some additional cash.

Does Owner Liability (CVC 17151) apply to a vehicle that is registered out of state?

Where the accident occurred would be the controlling jurisdiction. Their laws would be applicable.

Yes. As long as the video has not been erased. Request it thru the Freedom of Information Act.

What do I do after rear ending a car on an ongoing traffic street and then getting arrested for dui, driving a friends car?

Turn the matter over to your insurance and allow them to handle it.

I need some help after a car accident (all property damage) after the insurance company low balled my quote to fix.

Your options are to accept the offer, negotiate to get more $, hire legal counsel to assist or file a law suit.

What should I do about a debt from an accident?

Talk to local counsel about what was signed. Your answer to your liability is likely within the document.

What is the worst case scenerio for this type of situation?

Turn the matter over to his insurance. They will retain representation on his behalf.