Hi,
I'm not an expert, just a mother who a few weeks ago could have written your post verbatim, except my DS was 4 months. What was recommended to us was the following:
Break the nursing prop. This was REALLY hard, especially with the short naps. But it meant shh-patting/PUPD to sleep at every NW and at the start of every nap. The moderator also suggested trying to resettle after short naps with this is possible. I've been really just focusing on extending one nap a day - the rest are still 30-45 minutes, but these past few days, we're up to 1 longer nap (2 hours - heaven!). Instead of trying to stick with a 3.5 hour EASY, which was recommended for my DS's age (but impossible with short naps), I went with the philosophy of don't feed him right before or right after a nap. So he gets up, about 30 minutes later, I feed him. Since I stopped feeding him overnight, he has been eating SO much better during the day (he wouldn't eat anything at "breakfast" either!).
Nights - I committed to this at night, but it was rough for more than a week (didn't help that DS also got a cold in the middle of this!). It took hours of shh-patting/PUPD to get him to sleep. And his desperate and pitiful crying almost broke my resolve. But, 2 weeks later, he is much better at resettling when he wakes up. In fact, he has STTN for a couple of nights in a row. Oh - and moving his bedtime to 7:00 (ish) really helped too, for some reason. But it's creeping later again, and he seems ok, so I don't know if it was just a coincidence.
I've kind of ignored the "schedule" element of EASY, because like you, I couldn't predict or figure out exactly when he was OT or UT. Mostly, because of the short naps, I decided he was OT, and watched for any sign that he was tired. If tired, I'd start the wind-down routine. Someone else posted that walking was a good calmer, so I always started with 5-10 minutes of just wandering around my house, singing quietly. With extra winding down, my DS was calmer, more open to sleeping. (Most naps are still really short - we're still working on this!)
And we're going with the daily pattern that works for us - I have a drop-off and pick-up for my older DD as well, so DS often falls asleep in the car (short nap) or has a nap postponed (OT). It's a work in progress.
But since I broke that nursing prop, things have gotten SOOOOOO much better (although they had to get a lot worse first, I'm afraid). I understand about not wanting to wake up your DS1 - do you have family or friends who could take him for a few nights? Or a partner who could even do something like camp out in the basement with him (popcorn and movie sleepover with daddy)? We just shut all the bedroom doors and hoped for the best, and DD mostly slept through it.
I don't know if this helps, but please believe me that I was there too. It will get better! Good luck.