Update on my end. We finally switched our almost 16 months old to 1 nap over the weekend. Result is encouraging!
He refused to nap on Sat morning, so I made up my mind and let him stay awake til noon. Napped over 2 hours, then stay up til bedtime no problem. Unfortunately he was awake on and off from 3:30-7am. We were both dying on Sunday and he only napped 1.5 hours that afternoon, so we had put him to bed around 7:30 and the AMAZING, LEGENDARY 11-12 hours night sleep HAPPENED! He slept til 7:15am next day! Woohoo!
Saturday
Woke at 6:40 am, napped at 12:15, woke at 2:30, bedtime asleep around 8pm (Multiple wakings from 3:30-7am)
Sunday
woke at 7:00 am, napped at 12:00, woke at 1:30, bedtime asleep at 7:30
Monday
woke at 7:15 am, napped at 12:35, woke once around 1 hour mark, then rocked back to sleep til 3pm (had to wake him), bedtime asleep before 8pm (Spent 30 min to settle to sleep)
Tuesday
woke at 6:30am, napped at 12:10, sleep til 2:30 (had to wake him again), will try to bedtime at 7:30pm
Now I have a question, should I wake him from nap if he slept pass 3pm? It seems to be more difficult for him to settle for bedtime if he slept pass a certain time.