Hi,
First of all, in terms of copyright: Everybody can make a minimod for FH2 and release it, as long as it does not contain copyrighted material from other developers and as long as it requires a valid installation of Forgotten Hope 2 to run.
In order to join the FH2 team, you need to apply for a developer position. For that you need to show us models, animations, maps etc. that you have already made in the past. If we like what we see, you are made an applicant and are given a project to work on that you need to complete to our satisfaction. Once that is done, you are made a developer.