When the British MEPs go to Brussels they will separate and go into blocks - Labour will go to the Social Democratic group along with the SPD, and so on. The Greens will all sit together as a block (with a couple of exceptions). The Greens are, by far, the most cohesive group there. Your whole host of eurosceptic groups are a motley collection - a coalition of losers with no real unifying ideas. Your friends the Front National and the AfD are Eurosceptic but they do not have leaving the EU as their goal - they just want to change it. The other factor is that we do not know how long Britain will be there for, and nobody is going to go into partnership with, and make plans with, a group which may well only be there for 6 months. They are joining a Parliament which they would like to see destroyed, and that is a different starting point from the other Eurosceptic parties who are on the path of reform from within (albeit a highly undesirable reform). Your friends in the Brexit party will warm seats in Brussels (or more likely in wine bars) simply embarassing everyone.