Website layout and text size placements change on different computer screens.

I am currently designing a website for a friend and when we were finished we were testing the site and for some reason on his computer allot of the text and imagery was not align and out of place. We cant figure out what the issue is and why the websites layout gets disrupted. He has a 13inch mac and I have a 15 inch mac but in the past I have not had issues with this problem. Only thing I can possibly think of is because we are using a custom fonts and some code for stylizing the site? But like I have said I have not had these issues in the past like this. Let me know if there are any ideas or suggestions with how to fix this problem. Thank you! 

Here are some photos for reference of our issue.