DNS delegation to a GTM sync group

Hi, I've an average working knowledge on GTMs and have been exploring on how or in fact if a GTM in a sync group could delegate a query to another. I've had no luck so far. The setup contains an infoblox with three NS records to the three GTMs in the sync group. If I were to remove a GTM to make sure no query reaches up to it in case of a disaster or maintenance, would removing the NS record for the particular GTM on infoblox suffice or I have to remove it's NS record from named config/ zone file too on the GTMs? Any help on the topic is appreciated. A link or reference to a documentation explaining the flow would be of great help. * The GTMs are running on 10.2.4 HF version with named enabled and zrd disabled. zrd is enabled usually only when we're to edit the zone files of course.