adding new Posts in an array

I have created to post POST1 AND POST 2 n both have different categories.
i want image, heading n excerpt to be displayed in my home page. My problem i m unable to display both posts randomly.
suppose. i have 10 titles in POST1 and 4 titles in POST2.

i want to display title in this way in my home page.
title 1 of post 1
title 2 of post 1
title 1 of post 2
title 3 of post 1
title4 of post 1
title 2 of post 2.
……

please help me in this a