Run double async tasks at the same time

I have one Async Task that execute in ContentPage A, and another Async Task that execute in ContentPage B. Both of the content pages I gathered them in TabbedPage.

How to execute both the Async Tasks in both content pages when I open the TabbedPage? Because currently, the Async Task in A is executed completely but the Async Task in B seems like executed half way. The result in B does not return to the callback class.

Is this the correct way to completely execute double async tasks at the same time? Are there any other better ways of doing this? Can suggest me suitable links for understand asynchronous tasks?