1) Is possible for me to participate in royalties when the track is licensed to other labels?
No. You have to create your own original music to do that. You can't re-make
a Frank Sinatra or anyone else's song and start collecting their royalties.
That's the whole purpose of copyright. The original author of a song or
title copyrights his or her composition in order to protect against anyone
stealing their royalties, collecting their royalties and to receive their
royalties.
2) Is it possible for me to maintain ownership of the remix?
No. That's the purpose of the fee. You can retain ownership of the remix but
you and only you will be the only one to hear it. There is nothing you can
legally do about releasing it. It's not your copyright to control the
outcome. DJ's and producers get paid flat fees to remix another people's
titles or compositions.
Imagine if everyone woke up one morning and just started re-making
everyone's tracks and thought they copuld get paid royalties without
creating there own music. "I'll just copy this song and maybe I can start
collecting royalties from it's sales, Frank Sinatra won't mind."
Remixing is basically something producers and remixers do to
a) make a flat fee for their remix (you never owned the rights to the title
to claim anything)
b) get their name out to other companies in hope that people like what they
hear and may hire you or someone else to start producing their artist
c) it's usually a faster way to get some sort of production deal when you
re-produce a track everyone is familiar with
You do not have the right to copyright an already copyrighten work. It
already has ownership.