Its Lampings LAFD Rambo he made awhile back. Not for Public Release.
No as it is made for FiveM. Use LML if you want it in Singleplayer.
Siren is a private one since it took awhile to find and get working.
They do. CA only doesn't permit it unless the vehicle has a secondary siren or a horn that doesn't interrupt the siren. Hence why LACoFD and LAFD use to run Two Tone horns.