You can usually sign up to +5 additional guests (excluding yourself) for the guest list on any given night; just add the numbers to your name during the standard guest list sign-up process.
The limit of +Ns you see in the app for an event is set by the club, and Discotech cannot alter that. If you have more people in your party than the number of +Ns listed in the app, then you will need to ask your friends to download the Discotech app and sign themselves up. Everyone should have our app anyway!