You can have as many teams as you want, the only limitation is that each team should have at least 2 members. The same university can have 2 teams from the same department or a joined team between two campuses. It depends on your ressources.
Also each country who has more than 3 teams must organise a national qualification to select 3 teams to represent said country at Eurobot contest. This qualification round should be organised by a national committee (from university, association or another organism) registered as in the Eurobot consortium. There are already 11 committes, list here: https://www.eurobot.org/contacts/
For more information you can email at email@example.com and a volunteer (like me) will answer.