I need to create a custom finance control application for the company I work with and wanted to know if it is possible through some mechanism to create a database in firebase to be used in android, web and pc, in an integrated way and in time real.
I ask about the pc, because I do not want to use the web all the time (depending on the internet), because I want to use offline in all devices for use in estimates and report generation.
Any tips?
You can integrate firebase into both node and java, and you can do all the types of applications you mentioned above.
Here is an example of a java application with FireStore ("New Firebase"): link
Consider creating your application in Delphi , it can interact with a Firebase database locally and remotely, in addition to through the framework Firemonkey you can create and import your application in several formats for desktop and mobile.
Here is an example of how easy it is to work with Firemonkey databases in Delphi:
.exe or in some PATH listed in your OS (eg \ SYSTEM32) TFDConnection component of your tool window 
FDQuery component and with it you can make the calls through query's sql. FDQuery1.SQL.Text := 'select * from tab where code = :Code';
FDQuery1.ParamByName('code').AsString := '123';
FDQuery1.Open;