Okay, to summarize the debate we had in chat. Hopefully i remember this all correctly.
Yes, Isaac can turn on the shields, which block all solid matter, including living beings. However, the doors being open causes the cling shield to have a local malfunction, allowing crewmembers and potentially attackers to enter or exit.
The turrets have no auto-targeting system, but they do have video feed, allowing Isaac to effectively control them. The actual gunner crew is on board, but Isaac might get a few shots off before they can get to their stations. That's for Drake to judge, i guess. The turrets are pherza machine guns, meant mostly for use against fighters and other small spacecraft. They're mounted to the sides of the Exeralune, so only one can currently fire at the attackers.