African ethnic groups played just a big a role as Britain did. They were the ones that translated languages, knew the back roads and shortcuts, thought it was a good idea to sell 40 people for a single bottle of wine and a umbrella (look up Badagry, Nigeria if you think I'm making that up), etc. Look up Madame Tinubu as well.
Yes they are just as responsible. But realistically at the end of the day, neither Britain or Africans are paying out a single penny in reparations. This is real life, people don't do things because it's the "right thing to do". If that was the case slavery would've never happened in the first place.