subdomain – What’s the best way to setup analytics for a marketing website with SaaS apps?

We have a marketing website on primary domain with a SaaS web app on a subdomain of primary.

We have firebase setup for the Production environment of the SaaS product which includes ‘Web’ , ‘iOS’ and ‘Android’ Apps all connected to firebase PROD project. This PROD project is also connected/integrated with GA property. So all apps are working fine and recording analytics data atm…

However we’d like to have the marketing website and apps seamlessly integrated so we can track the full funnel from initial web visit and conversion through to all web/mobile app events so we have the full picture from pre-signup to post-signup in one analytics project/property. I’m assuming that’s the ideal way to go? So you can see conversion event on website, and track funnel all the way through to any web app or mobile app conversion events, tracking any bounces etc. along the way.

What’s the best way to go here?

Do we just re-use the tracking code/sdk used for the web app and install that to website so marketing website and portal (web app) are tracking same data? Will that even work when one is primary domain and the other is on subdomain?

Or would you add another ‘web’ app to the firebase PROD project for tracking website/primary domain individually? But within firebase you’d still be able to track full funnel somehow from website app instance through to SaaS web app or mobile app instances?

Would love to hear your thoughts as I’m kind of fumbling around in the dark atm. There’s not a lot of documentation or reference for these kinds of setups yet, especially considering web+app is kinda new/in beta.