We had a similar thing, although a smaller age gap (20 months). I did almost exactly as you are doing, but a very good sleeper, who went very happily into his cot every night was crying, asking for drinks etc. And waking in the night. Basically I tried to keep his routine intact, and effectively it was the same as yours except that they were both put to sleep upstairs. Things settled down with persistence. I did give him more hugs etc. in thr night, when he asked, because I thought he must need the reassurance but there came a time when he seemed to be taking the p**s and I got tougher and it's fine now. And I am often on my own, so I had to have a routine I could do on my own. Now if only I could get him to stop takin off his nappy at night!