iframes if you really want to so the exact pages as given in App2 and App3. The pages in APP2 and APP3, give them a value in page-property ‘url’, say ‘forApp1’ and then should be approachable via <APP2’s url>/p/forApp1.
But preferable, of possible, would be to api-call App2 and APP3, only receive the data, and create the page in APP1