Yes, those 1-2 wake-ups are very manageable, and if you’d offered me this schedule when she was waking every 1-2 hours and I had a big deadline at work looming, I’d have bitten your hand off.
Our cot is just a regular one with one long side not installed, but the cot attached to our bed instead. You can get instructions for doing this online, although you do have to be careful it’s well attached and there aren’t any gaps where the wee one could get stuck. It’s actually a cotbed, so I usually lie down with her in the cot to feed her and then just get up once she’s asleep. If my husband is putting her down, though, he can put her in her cot and lie on our bed and get her down with just a bit of pat-shh. (We’ve only tried this in the last few weeks.) She does whinge a bit about this method, but it’s whinging, not full-on crying, and only a few minutes.
I tried naps in the cot at the same time because if it didn’t go well, I found it easier to deal with that at nap time rather than at night, and actually, it went better than I expected. She was used to being in the cot awake, though, so if your boy isn’t, perhaps read stories or something in the cot for a few days before asking him to sleep there.
If he’s going down for a nap at 11.30, is that his one nap of the day? How long does it tend to be? If it’s not very long, could he perhaps be overtime by bedtime? Supposedly that can lead to difficulty falling and staying asleep, sort of tired but wired.
Would your husband wear earplugs at night so at least he’s getting a better night’s sleep (if he doesn’t need to be able to hear your eldest)? I can’t stand sleeping in them personally, but my husband is fine with it.