In SP2010 it's done as the image above is shown, just separate the email-addresses with a semicolon. But in SP2013 I'm not getting this to work, is there a way around this? I need two users to receive the access request emails.
In SharePoint 2013, you can enter only one email. https://social.msdn.microsoft.com/Forums/sharepoint/en-US/cece08f5-20eb-49a2-9106-8443d71a2e39/email-access-requests-to-multiple-emails?forum=sharepointgeneral
I know it's not exactly the fix you wanted, but I always recommend access requests go to a shared mailbox, rather than an individual account, as this way: 1. Multiple people can access the requests (as per your requirement) 2. If/when you leave the company/team, you can just give new the person access to that mailbox, and do not have to change all the access request settings in your sites and subsites.