C.W.
I had some of the same issues. My sons schedule is
600 - wake up
730 - breakfast solinds
900 - nap (1-2 hours)
1100 - solids
1200 - nap (1-2 hours)
200 - bottle
500 - dinner solids
630 - bath time, lotion time, book time, and breast feed (or bottle)
700 bed
My son eats ALOT during meals and has been. He was waking up every 2/3 hours to hang out. I would even have him co-sleep with me because I was so tired. Then one day I had had enough and let him cry it out. He cried for about 45 minutes at a time. But finally got it after 1 week of doing it. Then he got ill and it was back to the drawing board because he was up sick and I wasn't going to let him cry when he wasn't feeling well. When he was better I let him cry it out 1 night and WAM back to normal. Now he sleeps 11+ hours a night and I get some time for myself. THings I learned through the process.
1. IF you go in and check on him don't talk more than just a nighty night or a hello/you're ok.
2. Change diaper only if you can tell their is poop
3. Keep a specific bed time routine so your baby knows it is bed time- if you sister can't be consistent at least you can.
4 When you get home from work make sure you are spending quality time - better than quantity. - less need to hang out in the middle of the night
This worked for us. If you are against letting him cry it out I don't know much other options, maybe talk to your dr. Mine said it was ok and that he didn't need the food during the night he was big enough. Do what feels right to you.
Good luck :)
C.