Where on Earth are you getting the idea that Trump doesn't own Mar-a-Lago? (Is this new rightwing humblebrag propaganda about their cult leader? I confess I've long since given up on keeping up with it.) It's owned by The Trump Organization - a collection of shell companies of which Donald J. Trump, so-called President of the United States, is the sole or principal owner; Donald Trump claims to have handed over
leadership of the organization to his children, and while
there are reasons to doubt the complete truth of that claim (for example, his sons are still Executive Vice-Presidents of the Trump Org, and while Donald is now listed as Founder instead of Chairman and President, no one else occupies either of those titles), there certainly has been no public or announced transfer of ownership to anyone. Are you alleging that Donald Trump himself is an employee of the Trump Org, and that it and he are secretly owned by some other person or group, such as a collection of shady Russian oligarchs? (That seems at least plausible, but there is no public evidence for it beyond the circumstantial.)
As for impeachability... this is about as impeachable as it gets:
Article II, Section 7 (one of the two Emoluments Clauses in the US Constitution (the other is the
Titles of Nobility Clause), both of which Donald Trump has always been in violation of) states, And, to head of the excuses,
the legal definition in US law is very, very clear,