I agree to a point. And it may well be that Brands has the final say on players. But I'll think you'll find that he and Silva work together on bringing players in. Brands won't bring anybody in (to the first team squad) without agreeing it with Silva first, and Brands will run the rule over any requests from Silva.
If Silva suggests to Brands that he wants to take another look at Vlasic in the summer, I can't see any practical reason why Brands would be against it. Unless you consider Vlasic tipping Liverpool as one of the favourites for the Champions league as being a practical reason.