Evidence admissible to court

Both witness testimony (hear and see) and video recording can be used in court to prove "someone did something".   Your tenant hears the party, and hear the eggs hitting the house, but he did not see WHO threw the egg.  You cannot sue everyone in that party, you have to name individual persons.  Therefore, so far you don't have very good evidence.

Even if you have evidence, there are two ways to sue them.  One is go to police, and have district attorney office to press charges.  For these minor crimes, they probably won't bother, because the burden of proof in criminal case is "beyond reasonable doubt", that about 80-90% sure the defendant is guilty, if the evidence is not strong, the district attorney won't press charges.

Alternatively, you can sue your neighbor in civil case.  The burden of proof in civil case is only "preponderance of evidence", (> 50%).  It is much easier for you prove your case.  However, what damage can you ask for in a civil case?  just some cleaning cost, less than one thousand, and the problem is not solved. 

I am saying all these not to imply that it is a plausible option for you, just trying to explain things.  Your best option is to learn some conflict resolution skills instead of hoping there is a legal solution.  Neighbors are living side by side, there is no legal solution in the world to solve their problem except one party sells.