TheFork users who ate in Hamburg have said really good things about Rossio | Tapas e Vinho, 1700 Tapas & Wines and Del Sur. Maybe you should give them a try!
Some of the more popular Spanish restaurants well suited for group dining in Hamburg according to TheFork users include:
Del Sur, with a 8.7 rating
Avelino Tapas y Vino, with a 9.3 rating
La Paz, with a 9.3 rating