A: This is an interesting question, but probably not one where you will find a definitive answer. In particular, if the tree is within the airspace and poses a danger, property ownership of the tree may not be the sole determining factor for who is responsible for it. Any answer would probably come from the case law, not statute, and there may not even be a definitive answer.
A: It would be very difficult to prove that a beneficiary designation was changed due to mental capacity or undue influence. Basically, whichever beneficiary is on the policy is unlikely to be changed after death. A lawyer would need to investigate the facts and case law for a more specific answer.