I already have a TWA app for my root domain which takes user to the home page. I have another page in the same domain and I want to target this as a landing page via a new TWA app.
https://developer.chrome.com/docs/android/trusted-web-activity/multi-origin/ - This will not help as the landing page for the two TWA apps are different.
As the web-server hosting both pages will share a single manifest file, I don't see a possibility of setting start_url attributes differently for 2 TWA apps.
Are there any alternate ways of achieving this?
I am no big expert on the subject (In fact I myself came here to figure things out).
But I have implemented four different TWAs in one domain. So, yes it is possible. You need to give different "launch url" (or android.support.customtabs.trusted.DEFAULT_URL) for each of those.
Not sure why you say manifest file will be common. My all PWAs have different manifest file, and so do corresponding TWAs.