Update Legacy WordPress Multisite & Plugins (PHP 7.4 to 8.4)

I have a legacy WordPress Multisite (Network of 3 sites: EN, ES, FR) running on PHP 7.4. I need a developer to modernize the stack on a Staging Environment.

The Project Scope:
Theme Switch: Replace the broken "Magnium" theme with a lightweight, compatible theme (e.g., Generatepress or Greenshift) for all sub-sites.
Preserve Content: Ensure existing WPBakery page layouts load correctly in the new theme.
PHP Update: Ensure the entire network runs error-free on 8.4 or 8.5.
Plugins & WordPress update
Fix any post update issues

Specific Requirement: The site uses MultilingualPress 2. This must be updated to Version 3 using the official helper tool (I have the license). Do not simply click update on this plugin.

Requirements:
Must have experience with Multisite Networks.
Work must be done on the provided Staging server first.
No SEO loss

Note: Please note my budget is fixed, don't place fake/spam bids or you will be immediately reported, Only apply if you can do this in my budget and have deep understanding of WordPress, multisite and PHP. Not just click on buttons but knows what they are doing and can fix any post update issues.

#Low Price will win