E.B.
Wow, that must be very frustrating for you. I'm not seeing how gating him in and letting him cry would make anything better, though--seems like that would make his nighttime fears worse, and will certainly result in you getting less sleep. It sounds like he really needs you to help him get through these nightmares. How about taking him to a toy store and letting him pick out a "protector" toy? Also, you could try painting or putting a sticker of a superhero (his choice) above his bed, along with a nightlight, so that he could see it and feel protected from his fears when he wakes up. Does he sleep in the same room as his sibling? (My family co-sleeps, so my first instinct is to say well, let him get in bed with you at 2:30 and spend the rest of the night there! You'll all sleep, and since I see you work, you'll get some extra cuddle time too! Or you could make a little bed for him on the floor of your room, and tell him he can come in and lay down without waking you up.)