I wouldn't say that Bilbao was against Nico Williams joining Barcelona because Nico Williams has the final say and decision to make. It's just that, Bilbao does not want installmental payment on one of their best players, because it's not a good way to do business and I support them. How will Barcelona be in a rush to get a player without being prepared. Bilbao did the best thing, if you ask me.
Wrong. Bilbao was against Nico's move to Barcelona. That's the reason they were also complaining to the La Liga regarding Barcelona who approached Nico. However, they're lucky enough caused by Nico rejected Barcelona because they can't guarantee to register him as a new player.
So he turned down Barcelona's offer, then extend his contract in Bilbao. This is the reason why he decides to stay in Bilbao much longer.