As a practical matter, it is up to you to prevent encroachment if you feel that the boundaries have been violated. You should get a survey to...

How do I notify a neighbor that they are not allowed to approach or harass my houseguests?

You should hire an attorney to send him a cease-and-desist letter

Does the neighbor really have easement rights?

Don't buy the property if you want to avoid legal issues

Should I contact a potential witness in advance of divorce trial.?

It is always best to contact potential witnesses, if you want them to testify in your favor. if you just list them, you don't know if they will...

What should I do after an attorney tried to represent the other side in small claims court? Could this be misconduct?

Most likely, an attorney who is not employed by the defendant will not be deemed as an "agent." You should continue to object to his representation...

Can I sue someone for getting them a car and they don't pay and it gets auctioned and now I owe the remaining balance?

Yes, you could sue for breach of oral contract (assuming the 2-year statute of limitations has not expired).

Marriage settlement

It could be handled through a default proceeding, but without knowing more information it is difficult to say how to handle this. Talk to a lawyer.

Is it legal for the parent of a child to place a tracking device on child while they are in the care of the (ex) other parent?

Not sure what you mean by "partial custody," but the issue of a tracking device is separate from the issue of the father's right to take the child...

Are pre-existing documents shared with a 3rd party and contain no attorney work product discoverable?

Based on what you say, my opinion is Yes.

Possible lawsuit against restaurant corporation?

Your best option is to contact the CA Labor Commissioner and see if they can represent you in this. Hiring private counsel is another option, but...