In other words, there is no 4th Amendment issue among private parties, and "reasonable expectation of privacy" does not apply to private parties where there is no government action or actor, to my knowledge.
I don't know if there is a statute prohibiting private parties from engaging in the type of behavior described above. If there is such a statute, there may be a violation of it. If there is no statute, there is no violation.
That's my guess.
Good Luck.