I run a web hosting service and have lots of experience dealing with site cleanup.
Once the site is cleaned, we can request a review from Google and they will clear it within 72 hours.
Part of my task is to replace Wordpress, all themes and all plugins.
If modifications were made to theme files themselves and not to a child theme, the modifications will be lost. If this is the case, it will need to addressed by a front end guy.
I advise that you delete any unused plugins, once the sites are clean and secure.
To do the job, I will need the following information:
Domain affected.
Hosting panel login/password.
Wordpress admin login/password.
SSH admin/password (If available)