Hi K. -
your not a bad mom to let your child cry for a bit....kids get it - they are smart! I have 4 kids, they all went through this and they all survived (and I let them cry!). My grandma used to say they were 'singing to the angels'! :) I wonder if you could maybe put a fan or a noise maker in your kids room, and then leave both kids in there. If your older child wakes up, go in and tell him that its okay, babies cry once in awhile but he is a big boy and doesn't have to wake up everytime the baby does. My girlfriend JUST went through this, she has a 2 yr old girl and a newborn, her 2 yr old was waking up a everytime the baby would. She told her daughter the same thing and she was like -okay, and hasn't been waking up since. She thought since the baby cried she should cry. Anyway, with 4 kids, we are BIG believers in noise makers/fans..it makes everyone sleep time better!! Don't be hard on yourself, do the best you can and do what works for your family!! If your kids are happy and healthy (and they sound like they are), your doing a fantastic job!