UX between app and Website

We currently have an app with certain features such as Timesheets and Booking holiday which is fundamental to our workers.

However we also have a live website which has all the other content that is relevant to our users such as internal News etc

The task is to bridge the gap between the two platforms

So my question is this - is there an generic approach for a UX, navigationing features between the app and Website, or is this just a big no no? Until we have the app developed?

And also each platform requires a seperate log in to make it an even uglier UX

I cant see how this will work unless its app > app or Website > website?

Any advice on this or reasons to push back on this would be greatly appreciated, as i have not come up against someting like this before..

Thanks in advance