The defending team has no right to request anything at a free kick, given that they are the ones that have committed the offence - but there is a requirement that they be at least 10 yards away when the kick is taken. If they are being slow about retiring the required distance then it's part of the referees job in managing a ceremonial free kick, to ensure they comply with the law. If some of them wish to stand next to each other then as long as you ensure that they're 10 yards away, there's nothing to stop them doing that.
At the same time, I'm not a big fan of the notion that the attacking team has the right to demand anything of the referee either (and it's true that the laws make no mention of this). They're not in charge of managing the situation, the referee is. Very possibly they might make some comment if the other team is being slow to retreat but as I mentioned, once you've made it clear to everyone that it's to be ceremonial and "on the whistle" then it becomes incumbent on the referee to take care of enforcing the required distance anyway. Neither of the teams should be dictating to you what to do, you should be firmly in control of the entire situation as regards both teams.