I found when my ds#2 got to around the 1yo mark & got interested in ds#1 toys, it impacted on ds#1's behaviour & he needed more Mummy time at bedtime. my 3yo has been easy to get to go to bed since 2 weeks after moving to his big boy bed & A LOT of that is we have a fairly long bedtime routine for him to unwind (anywhere from 2 -6 stories & I have found the less I feel like reading 6 stories usually means the more he needs the 6 stories
... he picks up on my mood A LOT) ... all my friends who have problems have no routine or one less than 10mins.
I think if you were to get your 1yo to bed & then devote 30-45mins of story time & cuddles to your 2.5yo (I know you dream of YOU time) I think you may find things change A LOT... also sleeping in his room for 3 days probably isn't long enough to change the habit (him getting negative attention) most books I have read look at 3 weeks as a reasonable length to change a toddler's habits.
As others have said, look at his whole routine, I'm guessing with 2 los (looking at my own life) limited one-on-one Mummy time is probably a BIG issue.
When you do get him into a routine at bedtime & wether you do WI/WO or gradually withdraw your presence, remember it will take time, but them more consistent you are the more effective it will be, the moment you "revert" then you are back to square one.
when I deal with a sleep issue I tend to say "I have a month to get this to work" that way I really do feel that I can have 1 step backwards at times.