I night-weaned DS around 20 months. He sleeps in the same room as us. He cried at night a couple times, but it wasn't too bad. I just explained that the milk was resting too & he could have some when it was morning/light out. Yeah, he woke up DP a few times, but he was able to go right back to sleep. We did not have another child in the room, though, that might be a little more difficult.
Could your DH & older DC "camp out" in another room for a couple nights? I'd think 2-3 nights might be enough. A spare room or even the living room couch might work. Just a thought . . .