Only an hour at 18 months? Wow! I train all my dck's to sleep for at least 2 hours...I don't get them up before that...and it's usually 2.5 hours, sometime even a bit more. Even the 3 yr old who sleeps for only an hour at home for naps, sleeps 2.5 for me and lies quietly on her bed once she wakes up. Is there any way you can move him to another room? Even put his playpen in a bathroom if there is space? That way he can make all the noise he wants, he won't wake up the others. I put my youngest/or worst sleepers in separate rooms. Within my playrom area, I have three separate corners with curtains around them for each of the others and I put a noisy fan on to block out noise. I find when one cries, it rarely wakes the others.