We have our room back! Last week we moved Walter in with Dean. I was a bit worried since I was still feeding him around 4-5 AM, but I so needed my room back.
It's surprisingly gone much better than I had anticipated. Dean has done really well. He's a much heavier sleeper than I have given him credit for!
The first few days I got up and fed Walt around 4-5AM so he wouldn't wake up Dean. Then I decided to just go for it and finish off sleep training. A couple of nights he cried and cried until he fell back asleep around 6AM for 40 min. nap. Surprisingly, Dean never came into our room when that happened.
I've basically stopped making Dean have quiet time if Walt's napping during Dean's old nap time (since I don't really have a place to put him). While it's not been ideal, it's worked out ok. They go to bed at the same time at night, and that's been nice. There have been a few days where Dean napped and went to bed later than Walt (and once where it was reversed), but he was really good and didn't make noises to wake Walt up. Dean's actually been much better at bed time and has only tried to come out of his room once in the past two weeks after putting him down. I think it makes him feel better knowing that someone else is sharing his fate.
Now they're waking up between 6 and 7, and while I really don't want to get up before 7, I'll take it because of all the other pluses.