I wrote to Firebase support, and here's their answer:
Hello there,
Thanks for reaching out.
Analytics data cannot be migrated from one account to another. You
also cannot export and import historical data with Google Analytics
for Firebase.
There are two way you could share the Analytics data to your Marketing
team
You can link your account to BigQuery and then use DataStudio to make custom reports which can be used by your Marketing team. Take
note that you can only export data to BigQuery starting the date of
the linkage so you cannot get BigQuery data for your previous data.
You can give your Marketing team's account a Viewer's access to your Firebase project. This way they can only see the data but will
not be able to edit or change anything in your project. You can see
this documentation for your reference.
Regards, xxx
I discussed the issue with my superior, and he agreed to giving the Marketing team Viewer's access to the original project, so that's what I'll do.
Hope it helps anyone else who's having similar issues.