We really struggled with Ben's sleeping once baby brother arrived. He kept getting out of his bed and yelling for us. I put one of those covers on his door knob so he couldn't get out of his room and did wi/wo. I know, mean mommy! We also got new Thomas the Tank Engine bedding, made a big deal out of it, put glow in the dark stars on the ceiling in his room, etc. Basically we made his room special for him. I think Ben was picking up on the fact that we stay with Charlie for him to fall asleep, we rock him, hold him a lot, etc. He was trying to get some attention!
It was really interfering with getting Charlie to sleep in his own room because Ben was sooo loud upstairs at bedtime. Now, baby brother goes to sleep first and I think that helped too.
Whatever you decide to do, be consistent and you'll get there. Ben now goes to sleep without any problem and sleeps through the night again no problem. Maybe consider gradual withdrawal since Travis likes you to stay with him.
It's so hard when you have to deal with a baby during the night AND a toddler! Hang in there!